Excellent. I've gotten snails, scuds, leeches, colonial rotifers, duckweed, Riccia and Ricciocarpus, a number of different insect varieties (mainly hemipterans, beetles, midges, and damselflies), and fingernail clams.
Just today I noticed a banded pygmy sunfish in one of my tanks who must have hitchhiked in two months ago! That was the prompt for this thread.