If you can, it's probably worthwhile running two filters anyway so that you have a backup in case one fails. Also, there's no such thing, really, as too much filtration!
Generally speaking, filters are capable of half the filtration they advertise -- so if you were to pick up a filter that's advertised for a 30 gallon, it's really best for a 15 gallon or less tank.
AquaClears are pretty easy to operate and decently priced filters. I'm running a 70 and a 30 on our 36 gallon and our water is always crystal clear.