I imagine many (most?) of you have already seen this, but for the sake of completeness I'm posting it here.

Wizards of the Coast (publishers of D&D) have for the past few years published one map a week for free perusal/download. Here's the link:

http://www.wizards.com/default.asp?x=dnd/arch/mw

I find this helpful mainly for inspiration, ideas (of both what to and what not to do), and a few "steals." Enjoy!