I'm a big fan of maps. When I get a setting book, the first thing I look at is the map. I don't know why, but maps are just really, really cool. That said, I do have my preferences.
Favorite rpg maps
Harn and Ivinia - Both are from Columbia Games. They are very detailed, and also make sense. Cities have lots of small villages surrounding them, and there are no deserts sitting right next to glaciers.
Forgotten Realms 1e - Yeah, they are pretty blank, and a glacier is sitting right next to plains and in a warm territory. But it's there due to a major magical curse. The wide open areas leave tons of room for me to stick in my own stuff, especially monsters. And the maps are huge, especially when you put them all together. Some of this is nostalgia, though.
MERP maps - All of them. These are works of art.
Earthdawn - Beautiful maps, that don't give away too much information. And the setting is quite different from standard D&D stuff.
Maps I don't really care for
Greyhawk 1e - I don't like the hexes. And most of the country names are downright silly.
Planescape - Love the setting. The maps are unusable in game, though they are pretty.
Wilderlands (Necromancer set) - Small, two-sided, hexes. I love the setting. The maps really needed to be bigger and in color, though that would have made the set ridiculously expensive.