I've used wonderdraft (and now dungeondraft) for a couple of years now and really like them. There's a little bit of a learning curve, but they turn out high quality results without much effort. As with most mapping software, there's always room for more art assets, but the ones that are provided are actually pretty expansive and useful.
I highly recommend at least checking out some of the results online.
Edit: Here's an example dungeon I created in dungeondraft in about 20-30 minutes, and another of a town I created in wonderdraft for my RToEE campaign. The town map likewise took probably 20-30 minutes.
Wow, thanks! That is high quality work!
I'll be ordering Wonderdraft later today.