I have the Marineland Penguin 100b and Aqueon Quiet Flow 10, both are great and I recommend them.
I still have yet to try the AquaClear 20, but its suppose to be really good and it's flow rate is adjustable.
If you can afford it you should try it, it's about $35 at retail price but if you have a Petsmart near you its on sale for $22.
They're all HOB power filters and they all flow at 100 gph (gallons per hour) The Marineland and AquaClear is rated for 20 gallons and the Aqueon is for 10 gallons.
Oh yea if you want to get an Internal Filter, I've also read good things about the Tom Aquarium Mini Filter.
It's rated for up to 5 gallons, flows about 45 gph and it's adjustable if I can remember.
Hope that gave you some ideas