Not all of these I necessarily agree with but they are worth consideration.

Backgrounds
Colour combinations of text and background that make the text hard to read
Busy, distracting backgrounds that make the text hard to read

Text
Text that is too small to read
Text crowding against the left edge
Text that stretches all the way across the page
Centred type over flush left body copy
Paragraphs of type in all caps
Paragraphs of type in bold
Paragraphs of type in italic
Paragraphs of type in all caps, bold, and italic all at once
Underlined text that is not a link

Links
Default blue links
Links that are not clear about where they will take you
Dead links (links that don't work anymore)

Graphics
Large graphic files that take forever to load
Meaningless or useless graphics
Thumbnail images that are nearly as large as the full-sized images they link to
Graphics with no alt labels
Missing graphics, especially missing graphics with no alt labels
Graphics that don't fit on the screen (assuming a screen of 640x460 pixels)

Animations
Under construction" signs, especially of little men working
Animated "under construction" signs
Animated pictures for e-mail
Animations that never stop
Multiple animations that never stop

Junk
Counters on pages--who cares
Junky advertising
Having to scroll sideways (640 x 460 pixels)
Too many little pictures of meaningless awards on the first page

Navigation
Unclear navigation; over complex navigation
Complicated frames, too many frames, unnecessary scroll bars in frames
Orphan pages (no links back to where they came from, no identification)
Useless page titles that don't explain what the page is about

General Design –(color)
Entry page or home page that does not fit within standard browser window (800 x 600 pixels)
Frames that make you scroll sideways
No focal point on the page
Too many focal points on the page
Navigation buttons as the only visual interest, especially when they're large (and dorky)
Cluttered, not enough alignment of elements
Lack of contrast (in colour, text, to create hierarchy of information, etc.)
Pages that look okay in one browser but not in another

Src: http://www.baddogdesign.com/webdesignprocess.html