A sweet looking set up like the one pictured can use a huge combination of different items to keep the water moving. If it was mine, I would use a small fountain pump with a length of tubing on the outlet run behind that awesome faux rock background. Then I would let the water trickle down the front of the background.
However, the best way to keep water from getting stagnant, pump or not, is to do regular water changes.
Over at Caudata Culture, we have a
page of various vivaria builds you may find helpful. While they are built with caudates in mind, many would be suitable for anura too. If anything, you may get some interesting ideas!