I've heard good things about the hagen aquaclear filters. I have a 110 (used to be called 500) coming in, got it for like $40 online. My old penguin 330 and 170 do a pretty good job, and was like $30 (the 330) when I bought it, but I'd like to step up the filtering a little more. Try to go for flow 10x the aquarium size. ie 50 = 500 gallons per hour.