You can get a clean up crew of bottom feeders that eat the leftover food if you over feed, but there really is nothing that eats fish waste. The beneficial bacteria in your biloligical filtration, once your tank has cycled will process the waste into items much safer for the fish (Ammonia (fish waste) goes to NitrIte (still bad) goes to NitrAte (much better)), but regular water changes and gravel vaccing are still a must. lots of people think there are fish that eat poop, but no such luck. Actually, it really wouldnt' help much, because those fish would in turn poop, and their waste would need to be dealt with. (presumably if they've gotten all the nutrients they can out of it, there would be none left if they re-ate it). I would say read the cycling info (if you haven't already) and come up with a good feeding regimen and a good water change/gravel vac regimen and you will be off to a good start!
Emily
Edited to clarify:
THere would be no nutrients left in the waste-eaters poop,so it would be pointless for them to re-eat it. Not that there woudl be no poop left if they reate it!