Usability checklist for site developers
http://www.WebReview.com/1999/10_15/strategists/10_15_99_4.shtml
webreview.com's 10-point usability checklist.
Heuristic evaluation
http://www.useit.com/papers/heuristic/
Jakob Nielsen's paper on heuristic evaluation (specifically for ensuring usability), which is basically the same checklist technique. Includes a ten-item checklist.
AskTog: First principles
http://www.asktog.com/basics/firstPrinciples.html
AskTog (a usability column) gives a list of principles for the design of a website or Web application, which could also be used in a similar manner.
Top ten new mistakes in Web design
http://www.useit.com/alertbox/990530.html
More mistakes listed by Jakob Nielsen.
Top fifteen mistakes of first-time Web design
http://www.doghause.com/top15.html
A list by somebody I've never heard of, but it's quite reasonable.
Lynx viewer
http://www.delorie.com/web/lynxview.html
View websites as they would appear in Lynx - use this to check your site is okay for text-only and disabled users.