The very first miniatures I can remember using in a D&D game were a pack of Slimes & Jellies. They were part of Ral Partha's Children of the Night series. I remember that I chose them because I wasn't very confident in my painting abilities. They somewhat resembled pieces of slag, and I figured I couldn't do too much damage to them even with my inept skills. I was actually pleased with the end result, which is more than I can say for the players who had to face them in the next dungeon I ran.