at Wal-Mart that has a ribbed carbon 'block" that forces air through it that supposedly cleans the tank. Are theses any good? I'll try to find a pic of it.

I'm pretty sure that you're talking about the The Small World Pump and Filter. (See link to pic below.) I've used this one and the main problem is that there really isn't any resevoir area for the good bacteria, and everytime you change the filter cartridge you tank has a "bio-filter crisis." I've solved this by replacing the cartridge, but then placing the old/used one in the tank also. On the plus side the filter unit does not take up much space, even if you put the used cartridge back into the tank. I use this one (for the moment) in my 2 gallon betta tank.

The other decent one that Penn-Plax has is called the Clear Free-corner cartridge filter. It offers a much better surface area for good bacteria growth. Also the filter pad can be ripped/cut off of a used filter cartridge and placed in the filter for added bio-filter surfaces. It takes up more space than the other one, but it works better, and comes in two sizes. The Penn-Plax web site claims that it can filter "aquariums up to 20 Gallons," but I wouldn't bet on it. I've used the clear-free filter with good success. If you decide to go with this type of air-pump driven filter this would be my choice.

Penn-Plax also has traditional corner filters, which would probably work well, but I've never used, and have no clue as to their size. You can see them on the same page as the clear-free filters.

Small World Filter Kit -- scroll down about half way

Clear Free - Corner Cartridge Filter

Good luck!

Yeah, the Small World thing was what I saw. I looked at them today and still forgot to look at the name! But, yes, that's what I saw.