Well the FHCO's and I use sketchup, as their artistic abilities are better than mine in the "drawing" arena.
They either find a reference pic of something they like, the 4E players manual has given them loads of fodder, or they find something on googles 3d warehouse, and have a go at it,,following the terms of service, of course.
From there they take the sketchup renders into gimp or photoshop, and run some filters to get a look they like.
They render everything big initially, and then rerender smaller versions once we figure out the scale, their plates started out as 1024 by 768 renders.
They have been giving maptools token tool a look, but I haven't tried it yet, or seen their results, but I do know they like it.
SeerBlue and the FHCO's