The fluval 404 is one. Maximum gallons it can be used for is 100 gal but as always more is better exspecially with these guys and one that preferably has a good amount of water that comes out of the outake due to dwarfs liking faster flowing water is better too. I personally think the best is just to build your own. It could cost a pretty penny but in the end is worth it. You can get a pump, filter fiber, some type of material with enough surface area to provide a way for bacteria to grow on it (also known as bio-spirals, bio-balls,etc) for about the cost or maybe a little more then a filter itself. One example is taking one of those water jugs for water machines, cut in half, take a piece of plastic grilling and cover the bottom spout with it, pour the "bacteria home" in, cover the top of the bacteria home with another grill piece then cover that with about a inch of filter fiber. Thats just a example of one. I have a kind hard time of describing what I mean in a message but you can get a idea of what I am talking about here
http://www.icomm.ca/reptile/filter.htm
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Jeremy Carroll
Center for Reptile and Amphibian Propagation and Conservation
http://www.onet.net/~eagle/Reptile/index.htm