You have a pretty good start, how about this?
- Valid XHTML & CSS
- Must work in IE6-8, FF and Chrome
- No inline CSS should be referenced as separate file
- CSS needs to make appropriate use of cascading styles
- CSS should have styles for ul/ol lists, h1-h4 headers, forms, blockquote, comment, etc.
- All image paths need to be relative
- All image files need to be saved for web in the smallest size without pixelating
- Design needs to be tableless
- Any javascript files need to be local (not referenced from other sites)
- Block elements need to be commented
- Menu structure should have CSS for first, active and last classes
- Documentation and style guide (classes for like alert boxes, etc)