Glyfair
Explorer
Mage knight figures work nearly just as well as DND minis....as you said,their bases are a little big, and they occasionaly have arms and such that stick out too far, they might not fit perfectly especially if its tight quarters, but they have alot of the iconic figures that you'll want for a game. If you have them USE THEM, there isn't any gameplay reason you can't, the scale isn't far off, nothing you can't ignore.
Also, the heroes from the first MK Dungeons set are almost exclusively old Ral Partha sculpts. Scale is about as comparable as any you'll get from using different companies figures of the same supposed scale (the figures can be inconsistent, just like DDM miniatures).
Also, there are a lot of MK sides sets that work well. The 3D dungeon tiles were priced pretty reasonably (although pretty standard, except for the traps set). The castle pieces look fine. The MK Dungeons sets had nice maps, some 3D terrain, etc.