I have the same book that silvereagle mentioned, but my favorite is Gold Coins of the World - from Ancient Times to the Present 7th edition by Arthur L. and Ira S. Friedberg. The Krause book only goes back to 1500, Friedberg covers them all For those that want high quality color pics - start collecting the auction catalogs. They are an excellent source for not only color pics but also research material, realized values and unlisted coins.
I got a complementary copy of the Elsen catalogue when i sold them my gold noble... and bought an Anglo-Saxon penny and a certain French coin from them. And i was greatly impressed by what's out there. Never had one of these auction catalogues before, it was an eye opener.
These coins have made me sick Sick with envy that is. The only gold ones I have from that country are a tad later than these. Neat coins. (hurl) Ian