I have had the best luck with waterfall type features using this type of pump/filter:
Whisper

There are a number of ways to incorporate it as a waterfall feature. I have had the best luck with Expanding foam such as great stuff, however, a bit of work with some pieces of slate and some DAP brand aquarium silicone are best. Expanding foam is too unstable in the long term to use in my opinion- it shrinks.

The thread on here I posted a while back about my FBT enclosure shows the use of this type of filter and expanding foam. The construction thread is on Caudata.org as "Caudate Bar".

You can utilize small fountain pumps ant tubing, however in my experience with vivaria, these type of systems clog up quickly in an enclosure that has live animals in it. They can quickly become more trouble than they are worth.

There are also quite a few OTS (Off The Shelf) waterfall features available at pet shops, however I feel they look rather unnatural. I am a huge advocate of realistic looking vivaria.