I’ve found these 25 points Website Usability Checklist, very useful to use when you are working in a web redesign project.   There are many things to evaluate: Accesibility, Identity, Navigation and Content.

Accessibility

1. Site load‐time is reasonable
2. Adequate text‐to‐background contrast
3. Font size/spacing is easy to read
4. Flash & add‐ons are used sparingly
5. Images have appropriate ALT tags
6. Site has custom not‐found/404 page

Identity

7. Company logo is prominently placed
8. Tagline makes company’s purpose clear
9. Home‐page is digestible in 5 seconds
10. Clear path to company information
11. Clear path to contact information

Navigation

12. Main navigation is easily identifiable
13. Navigation labels are clear & concise
14. Number of buttons/links is reasonable
15. Company logo is linked to home‐page
16. Links are consistent & easy to identify
17. Site search is easy to access

Content

18. Major headings are clear & descriptive
19. Critical content is above the “fold”
20. Styles & colors are consistent
21. Emphasis (bold, etc.) is used sparingly
22. Ads & pop‐ups are unobtrusive
23. Main copy is concise & explanatory
24. URLs are meaningful & user‐friendly
25. HTML page titles are explanatory

Source:  www.usereffect.com