Colorbrewer is a web-based tool that provides colour advice for your maps. Looks quite useful, especially for people creating choropleth maps and the like: it has colour schemes for sequential, divergent and qualitative data, with options for colour-blindness and photocopy-suitability. The development team was led by Cynthia Brewer, the author of Designing Better Maps and Designed Maps. Via geoparadigm.