http://www.webaim.org/
http://webxact.watchfire.com/
http://trace.wisc.edu/world/web/
http://www.rnib.org.uk/xpedio/groups...nib008789.hcsp
http://www.macromedia.com/macromedia...usablenet.html
Note that there is a ballance between accessibility and useability. Some of the more accessable are not all that usable. For example, http://trace.wisc.edu/world/web/ could really do with some work on useability.