I like maps that have lots of fun geographical stuff like impassible barriers (mountains, rivers), port cities that can take you many provinces away, lots of choke points, etc. I'm excited to see the thematic maps currently in production. The Faerun (forgotten realms) map for Dom2 was really cool, but it was so big after many turns I got a bit lost in it. Definitely a victory point map
The Europa map is also excellent. I am currently in a game as LA Man, and have having a heck of a time against the giants in scandinavia and Ermor in Italy.
Some ideas for maps, and might just only require good scanning skills: Westeros, a la George R.R. Martin. Shannara a la Terry Brooks. These wouldn't work thematically, but neither did Faerun, and it was still awesome. Someone who has the skills could port a lot of the Dom2 maps into Dom3 (I heard they sorta work, but some things were out of whack). A map of California would be fun.
Cradle of Dominion style maps rule all the rest though. Absolute excellently designed map.