i've been thinking about this small above the ground pond... It comes with a pump but not a filter... Any ideas of what kind of filter I can use with it?

http://www.tetrapond.com/catalog/product.aspx?id=358

Well, you could even make your own out of a sturdy plastic container like a trash bin. You just need to make holes for the hoses and add your own filter media.

I do recall seeing some a while ago. Check out the diy threads.