Warning these sites contain m/m stories. More links coming soon.
Desires
This is a wonderful JC/Lance page with mixes of Justin/Chris thrown in. All the stories are wonderful especially her Road Less Traveled series. Her College Life  series is good too, totally different from mine if you've read it.

Experiment V
Rhys' stuff is really awesome, at times it's a little weird but it's cool. She does all sorts of pairings and does them awesomely.

The Studio
CJ rocks! Every story on this page is totally awesome and a must read! The two chapter stories are long but rock!! Doppelganger is probably my favorite, it's just totally cool

JC and the Pussy Cats
What's better than girl!sync stories? Nothing? If you think so, check out this site. It has a nice collection of girl!sync stories, a few girl!bsb, even a girl!wade and a boy!brit

Pen's Playground
If you don't check out any other sites, I recommend this one. Pen's stories rock!! Check 'em all out!! Who's Your Daddy and Doggy Style crack me up something awful! This girl is hilarious!! 

The Closet
This is one of the best collections of Joshtin around. Good site.

What We All Wish For
This is a collection of Joshtin stories ran by Viv and Claudia. Their goal is to collect all the Joshtin on the net.

Diva Hips
These are some seriously awesome *NSYNC stories. I really just love them all.

If I Had It All
This is an amazing JC/Tony Lucca story! I really love it!! I heart JC/Tony right now so yah lol The other stories on this page are pretty good too, but this is my favorite.

Pretty Kitties And The Gang
Mya is awesome! She wrote me JC/Tony, I heart it like crazy lol Her newest stories, High School Sweethearts and Something Like Dharma are really good.

Sakeene
*N Soap (An Alternate Universe) is probably my favorite series. It's new, but I'm in soap opera mode.

I Think We're Alone
The Long Run is an amazing story. It is long, but very much worth the read. Chris/Lance

Nasty Boys
Cody is an awesome Joshtin writer. Everything is really well written, although he doesn't seem to like Lance at all.

Spread The Jelly
This is a must visit for any Jelly fan (Justin/Nelly) best collect of Jelly stories out there.

Lisa Chasez
Lisa Chasez kicks ass. Everything is worth reading!! Especially Chicago Days and LA Nights (CD's sequel) and Searching (punk!justin, AU)

Igby
Igby kicks ass. All AU's, mostly highschool universe. All are a must read!

Slash, Sparkle, Pop!
Good collection of stories, can search by just about anything.

Fictitious Library
Another story search page.