I'm really a fan of mystery snails, and I find that the black and Inca (yellow) tend to leave plants alone as long as they are well fed. They will eat any dead plant matter though, so they often get blamed for eating plants.
You might also want to throw in a few Malaysian trumpet snails in the aquarium. They are amazing at cleaning up any leftovers in the tank, and they also eat algae off of the glass at night.