+1 on the sponge filters.
But if you're more interested in a HOB-type filter, the Marina Slim filters are really nice. I have three Slim s10's on three seperate 5 gallon betta tanks and they have been great - two of the three don't even need to be baffled on the output (the third is for a very heavily finned dumbo halfmoon) and they come with a prefilter sponge. The AquaClears are great, too; many consider them to be the old workhorse of the aquarium trade as they have an adjustable flow, are extremely customizable for filter media, and are built to last ages. However, the smallest AquaClear is rated for 20 gallons and is therefore rather large for most betta tanks under 10 gallons.
Last edited by pittipuppylove; 12-29-2012 at 02:57 PM.