Catfish or Plecs are handy, Bristlenose plecs go well with just about anything and help keep your tank clear of algae, corydora's are good, loaches (clown, royal, kuhli) are good, clown loaches especially good for eating snails, and they are quite colourful too.
Fish which aren't good tank mates...
Aggressive cichlids , most knife fish (except black ghost knife fish), Arowana's, Pacu(Last 2 get to enormous size and outgrow just about any tank you might feasibly own).
The general rule of thumb for fish eating other fish is, if it fits into its mouth, it'll eat it.