Free Color picker for Windows XP/Vista

Colorpic is the best free color picker I've used. It allows you to capture a colour from anywhere on the screen and easily copy the RGB or HEX values for use in Photoshop or web-design.

HTML Color codes

HTML Color Chart - This page contains the names, hex codes and previews of web-safe colors - useful when in Photoshop or coding in HTML. There is also a few large size, print quality free colour charts available on the web - such as this one.

Colour Lovers

Colourlovers - Colourlovers is a great site for designers stuck for colour layout ideas. You can browse through user-created palettes or create your own by selecting your favourite colours.