Accessibility (Alt-0).  Web Design, Sheffield.

Usability

• Jakob Nielsen
• A list Apart
• Universal Usability Guide
• US Gov. Usability portal
• W3C Markup Validator
• W3C CSS Validator
• W3C Schools
• Lynx viewer

Accessibility

• WCAG 2.0 Techniques
• DRC survey report (PDF)
• DRC Press Webcast
• W3C WAI
• Vischeck
• RNIB
• Cynthia Says Portal

Other useful links.

• Webmonkey Developers resource
• favicon editor
• Browsershots Compatablity
• dotmobi Mobile Emulator
• Ampersand codes
• UK Small Business Directory
• UK Business Directory
• Internet & Web Development - B2BIndex.co.uk