You want at least 6-8' of head for a pump, and thats on the low side, but should be OK for a CPU only loop...The Via Aqua's and Hydor are 2 that some WC'ers use that are inexpensive...Be sure to watch for heat dump on the pumps, you don't want over 30W of heat dump going into your loop, any higher and it can hurt your temp's...What I do, and its just a rule of thumb, is to look at the wattage rating and figure about 3/4 of that will be going in the loop..Thats will give you just a rough idea because the design of the pump will have a lot to do with how much heat it will actually dump into your loop....
EDIT: I would be sure to keep aquarium pumps out of your case, they tend to leak..
Heres a link on Via Aqua silencing, the model # might be in there to I don't remember..How To silence a Via Aqua
If you want o do it on the cheap a Bonnie core is a real good rad for cheap...Barbs for heater-core-fstfrddy
....How to make a dual heater core fan shroud..