Desktop GIS - the book

The U.S. Geological Survey has an excellent poster on projections available at http://erg.usgs.gov/isb/pubs/MapProjections/projections.pdf. You can also download it from this site.

Another good publication is Map Projections: A Working Manual, 1987, by John P. Snyder. This Professional Paper contains detailed information about projections, including concepts, usage, and formulae. It is available in PDF format from http://pubs.er.usgs.gov/usgspubs/pp/pp1395.