Following the link on Dow's post, there is a whole series of articles and FAQs on tank plumbing by Anthony Calfo. Definitely worth reading. In one of them he strongly recomends against wake makers or powerhead timers. I love the return manifold idea on a closed loop. Between that and a couple of sea swirls, I think you could count on really good flow charateristics.

Still, there's no doubt in my mind that the most effective and healthy flow for a reef tank would come from a well designed surge device. This is an engineering project that our hobby could really use. I have an idea that involves a couple of cylinders with pistons. These would be plumbed to opposite ends of the display tank; one would push water into the tank, the other would simultaneously pull water from the other side of the tank. Then the pistons would switch directions in the cylinders, and the flow would reverse. The benefits are alternating currents, great water movement without the water ever going through a pump impeller, and a terrific surge without a net loss or gain in the tank water volume.

I thought about trying to build this, but I'm too busy. It's not too difficult to figure out though. You need a big cylinder, piston, and a worm gear.