Screen size @ AnyBrowser.com
This tool shows you how your web page looks like on various screen sizes.
Provide a URL and it will take real screenshots in different browsers of that page.
Web Page Analyzer
This service allows you to see what your pages will look like when viewed with Lynx, a text-mode Web browser.
Government regulations regarding electronic and information technology being accessible to people with disabilities.
Shows you how things look like to someone who is color blind
Effective Color Contrast & Making Text Legible
Designing for People with Partial Sight and Color Deficiencies
Color Code Reference at Web Monkey
Evaluating Web Sites for Accessibility @W3C
A multi-page resource suite that outlines different approaches for evaluating Web sites for accessibility.
Links about web usability
Color Palette Creator
A tool that allows you to input one base color and see a range of tints and shades.
A Flash based color scheme generator and picker. It generates complementary color schemes based on your inputted color values or random schemes.
Color Scheme Generator
Pick any color and see monochrome, contrast, triad, tetrad and analogic color palettes.
EasyRGB Color Harmonies
A complex color-picking aid that can help you find complementary colors. You need RGB color numbers (not Hex) to use this tool.