OnlineDM
Adventurer
The only issue I've found with MT and image based maps is that any decent resolution map is so large that it can easily take 10 minutes for all the clients to grab it and display it. I find that using the vector graphics for the bulk of the map and just dropping in images of whatever objects you need on top of that is more satisfactory performance-wise. Of course if you have client and server on the same LAN it doesn't matter much. You can also upload archives to a site, but then you have to have a place to put the archive that is fast.
I just draw my own maps using the drawing tools in MapTool, too, and I've been happy with the results. It does take time to create the maps, but everything seems to run smoothly.