Inverts:
Pond snails (Physas sp.)
Red ramshorns (not to be confused with Columbians)
Malaysian trumpet snails
They're not really pests but can be unsightly in vast numbers and proliferate rather quickly if food supply is abundant. If you want pets, try Pomacea bridgesii. If you're located in USA, only brigs are legal and you need to secure a permit to be able to ship them elsewhere. Other Pomacea sp. are banned for transport.
Fish:
Most livebearers will do. Convicts and zebra danios are pretty easy to breed.