Ahh, maps. Love 'em. Some stuff that comes to mind:
*As mentioned, Harnworld. I have an image of Venarive, North-western Lythia, which is just gorgeous. Don't know where I got it, though.
*The 4E Eberron map is gorgeous, one of my favorite computer-generated ones (I tend to prefer the more naturalistic look of hand-drawn).
*The 3E Forgotten Realms Campaign Setting world map is nice, if not great. But it is the best Faerun map I've seen.
*The Known Lands of Artesia. Good hand-drawn stuff. Cartoony in a good way.
*Cyradon has a pretty nice map.
*
Keith Curtis does some nice work.
*Someone has posted really great computer-drawn maps of Greyhawk on this site in the cartography forum. They really are the best I've seen of their ilk, but be warned: the downloaded PDF is very cumbersome to use! I also like the Greyhawk maps from the 1E set.
*Finally, there have been lots of nice maps of Middle-earth. My favorites are
here and
here, probably the most beautiful pencil-drawn maps I've seen.