So long as you keep them low in the water they shouldn't make bubbles. Hydors are good (I use them) but it's an equally good idea (if possible for you) to add another return pump but much smaller to give you another source of circulating water.
It's a lot cheaper to buy another pump and some PVC to shoot water around your tank than buy the Tunze, Hydors, etc.
You can get Hydors 25% or so cheaper than an LFS at foster and smith, but you might want to try out maxijets from the sponsor spotlight. I use maxijet pumps all the time because they're cheap and good and I bet those powerheads are worth giving a shot.