Back around 1980 I bought J.B. Post's The Atlas of Fantasy, and that really kicked off my life-long love for these sorts of maps. My list of favorites is way too lengthy, but it includes all of Shapiro's maps for Eddings' works, the Tolkien maps, the Pern map, and the Haff and Martin Oz maps.

Top of my list, however, would probably have to be Geoffrey Mandel's Star Trek atlas and Karen Wynn Fonstad's atlases; I've got Pern and Middle Earth, both of which are great, and I'd like to get her Forgotten Realms and The Land books.