I have used both the Natural Wave and Coralife Power Center "powerstrip" type wavemakers. Neither has four seperate channels, but you could run two powerheads on the same channel if needed.

Gary is right that these will most likely reduce the life of the pump, but the next step up in pump controllers (with soft start, etc.) is really expensive ($100+). The next increment ($) is a single external pump and a SCWD or OceanMotions. I now have both of these and far prefer them to switching pumps on/off.