Here are the links to the Official Sonic Sites:
Sega of Japan (Sonic Channel) The site itself is somewhat limited, but the game updates show up there about two months before they do on the US site. The character bios are quite good as well, providing you can understand the broken English. Strangely, there is a link to the US site from there, but there isn't a link from the US site to the Japanese one.
Sega of America (Sonic Central) This is definetely the better site of the two and half (keep reading) official Sega sites. There is a European one as well, but it's STILL under construction! Anyways, this site has a whole list of every Sonic game in existence, which is very impressive, as well as links to all the game mini-sites (I'm surprised they still keep them up!) It's also much easier to navigate around, and they have a feature that lets you listen to Sonic music from recent games. The bad news is this site hasn't been updated for a good 2-3 years.
Sega of Europe (Sonic City) :Now and then it opens up, but for the most part, it's "under maintenance". What I really love about it when it's up is the "casual" feel of it. If I didn't know better, I'd say it was a fansite! (At one point, I actually thought it was)
Chao page This page is no longer updated (and hasn't been for about four years or so), but Sega still maintain it. There are two different sites, the one in English and the one in Japanese. So far, I haven't found a difference in either besides the language it's in. In addition to being a chao page, it also has a link to the excellent SA2 minisite.

Links to other Sites:
Wikipedia Sonic Page There are pages on just about every major Sonic character, as well as all sorts of facts you'd never know otherwise.
4kids.tv Whether you like 4kids or not, there's no denying this is an excellent site in terms of Sonic information. When the site was "upgraded" to GameStation (some things were hugely improved, but I'll never forgive them for ruining the custom avatars!) episodes were added online. So far, only the first season is up. Anyone can view these, whether they have an account or not. They also have a section of plot summaries, which sometimes are inaccurate and/or hard to read. Still, I'll credit them for fixing "Emel" (in the show) to "Emerl" on the summaries. I doubt they'll go back and change it when they re-air those episodes.

Information: Sonic X: Uncensored! A truly excellent site containing changes made in all 76 episodes-with pictures!
Sonic HQ A good all-around Sonic site. The site itself is massive, and includes a large section on the comics and the shows. Sadly, it doesn't have too much information on the games. Its other major con is that it's CONSTANTLY under maintenance (and the staff don't seem to be getting anywhere, either...) Right now it isn't, but it was inaccessable about 3 months ago.
The GHZ (Green Hill Zone) While it's rather...empty in parts, what it does have makes up for what it doesn't. The game pages are very high quality, for what games they actually have pages for...
Team Artail They have a selection of the music from the games,and the quality is amazing. In addition, they have around 9,000 screenshots from Sonic X and news about Sonic in general.
SatAm Episode Guide (contains plans for Season 3) Self-explanatory. I figured I'd out it up for the benefit of the purists.
SonicStrike At the moment, the only part of this site that's available is the Sonic X section. It gives out good information, as well as featuring game/show comparisons and reviews/summaries of the episodes. Sadly, there are only a few of them.(UPDATE: The entire site has shut down/is under maintenance, so only one page is viewable)
Sonic Strike (main) Yes, this is the same site, just the main page. I posted it again since the main part is much better, and it's a pain to navigate around.
Sonic Downloads Sonic X episode downloads. I can't get any of the episodes to work, so I have no idea about the quality and very little about the actual site.
More Downloads See above.
Subbed Epsiodes These are fairly good quality subs that work pretty good, but I will investigate further later.
Decofranken.de Yeah, I know it's an odd name, but it's an awesome site. There is a good section on Sonic X and the comic, as well as some information on the other shows and some miscellaneous information. There is some information on Sonic Adventure, Sonic Adventure 2, and Sonic Shuffle, including reviews of the aforementioned games.
Sonic City (Unofficial) FYI, this is not the true Sonic City, but either way, it's a good site. Sadly, it has a TON of typos, way more than you'd ever find here.
Blue Blur Central Another good all-around Sonic site. It also has a lot of links to other good Sonic sites.
Sonic News Network While it's certainly no Mario Wiki, this site still has an impressive amount of information, even if some of it is directly taken (read: ripped off) from Wikipedia.
Sonic Heroines While I don't like to put up websites devoting to specific characters, this website focuses mostly on the girls of the Sonic series (WOOT!), though it has bits on everyone else. It's a fairly comprehensive website, including a personality test (though not as long as the one here), fanart, and more stuff.

Fun Stuff/Parodies Sonic Personality Test Team Chris While badly-made, it IS good for a quick laugh. I wonder where they got the Chris/Decoe?Bocoe figures, though? I thought only Shadow, Sonic, Tails, Amy, Knuckles, Eggman and even Big had figures.
Sonic School House Warning: THIS IS OBNOXIOUS
Uncyclopedia-Cream the Rabbit Read these at your own risk. You'll see why in a few paragraphs. There are articles for Rouge, Sonic, Shadow, Tails, and Knuckles, but Cream's is the funniest by far. Some of them are funny, others are just plain stupid.
Sonic Music(there is a fair chance it wont' work-sometimes it doesn't, sometimes it doesn't) If that doesn't work, just try putting this into the url box: ftp://ffmedia.defchamba.com/SONIC%20the%20Hedgehog%20-%20Music/ Chaotix Video A video composed of clips from Sonic X featuring the Chaotix. This is actually pretty funny. (NOTE: This video was removed, I'm leaving the link up still in case it's brought back. Sometimes it happens.)
Another Sonic Parody; I got a good laugh out of thisThe actual topic regarding the picture above
Name Generator-What Character are you?A simple little widget. Before anyone asks, I got Princess Elise.
Now THIS is hilarious! I'm sorry, I can't describe it any other way.

Guide To My Reviews:
Overall: When I review, I judge in three categories: Plot, Art (Visuals in Sonic X), and Effort. For more about these, see below. My final grade is the average of all the below-mentioned part's grades. Here is a basic quide to the grades:

10: Perfect	9: Fantastic	8:Awesome	7: Good	6: Decent
5*: Mediocre	4: Poor	3: Inferior	2: Awful	1: Outright HORRID!

*If an element is not present or is no more present than normal, it is included as a neutral 5.5.

Plot: This is how well the story was developed, how few plotholes are present, how interesting the story is, how creative it is, et cetera. Does the plot make sense? Is there a plot? Do the characters act IN CHARACTER? Is the story concept well-thought-out? That isn't to say there have been good stories with bad plots; often there are other areas that make up for it (humor is usually it). I generally find this works MUCH better on a show than it does in other media.
Art (Visuals in my Sonic X reviews): This is how well it looks overall. Are there any misdrawings? Miscolorations? Bits of excellent animation or special effects? In my Sonic X reviews, I generally leave this out or incorporate it into Effort. Occasionally, it will have its own section, and generally when it does, it's not a good sign.
Effort: This has two meanings:
1: Did 4Kids (Archie,TMS, et cetera) put any effort into this? Were they really trying to please fans or were they just trying to make a quick buck (or yen, in TMS' case)? Does their effort (or lack of it) show? Like with Plot, originality is a huge factor in this as well. Did they make an attempt to make a creative and engaging story? Was the plot completely original, or borrowed from other sources? Don't get me wrong, I appreciate a good reference/parody. I do quite a bit of it myself. I've made countless Sonic references in Eternity (the series I write) such as Twilight making a sarcastic crack about being the Ultimate Life Form (in the manner of "Well, if that's true, I'm the king of France") and Rivette's dramatic christening of a weapon "The Eclipse Cannon" (before being told that name was taken), as well as Mascara's insignia looking remarkably like Dr. Eggman's. Others were physical, such as a direct tribute to the flood scene in Sonic Adventure (I actually drew it from a videotape I made for 100% accuracy).
2: What makes the watcher/reader care about what happens? Is this factor present at all, even? In my opinion, there are two major sections of a character: their outer section (their concept, their design, their name, et cetera) and their inner section (their personality, their actions and how they affect the story, character development, backstory, et cetera). When a truly excellent character comes around, they typically have large amounts of traits from both sections. That's not to say all characters who have one or the other section as a strength are lousy characters, they can still be good. Let's look at some examples from the Sonic franchise itself. Take the Original Freedom Fighters (from Sonic the Hedgehog #142-143). I personally liked the way they flawlessly operated and not only acted as heroes, but had a strong motive behind their actions. Sadly, they flopped like kippers on a grill in the outer section (yes, I know that sounded paradoxical; don't rub it in). They had painfully unoriginal designs, and their names sound like they came out of Looney Tunes. Come on, "Tig Stripe", "Spot Long", "Sergeant Peckers" ?! (though Sergeant Peckers actually was kind of funny; I can't believe they got away with that name). On the other extreme, there are characters that look cool yet fail to deliver anything else to the series they're in. For example, Chaos. There's no denying a giant serpent made entirely of water isn't cool, especially once you see its/his actual appearance rather than read about it. Not to mention it/he's incredibly powerful and has an awesome array of attacks (not including alliteration). Despite that, it/he has very little motive behind its/his actions beside the obvious: because Sega said so. While maybe I'm being over-expectant here, considering Eggman, Iblis, Mephiles, Metal Sonic, and just about every villian in the entire franchise don't have too much going for them in terms of motives either, it's still a complaint of mine. Then there are characters who are very strong in both aspects (and there are quite a lot of them, too in the franchise); I happen to have one particularly in mind (consider my fangirlism and guess).