These are the overflow brand I use:
http://www.drsfostersmith.com/product/p ... atid=23781There's a small pump ensuring that you don't get a siphon break. Since it's tied to the same outlet that the return pump is on, I feel comfortable it will survive a power outage without flooding my floor.
Somewhere I posted pictures, but I can't find it. The refugium is on the floor. Effectively, it's like a canister filter, but the difference is the return pump is the driver. So long as your return pump can't add more water than your overflow can remove, you are good. The first return pump I used was too powerful. It didn't overload my overflow, but it just caused too high of a flow through the refugium.
I downsized a bit, and all was good. I remember when I was discussing this, some cautioned against an overflow. The danger is that the siphon on the overflow breaks, and the return water starts flowing over the edge of the tank. I'm a bit over four years in, and a few power outages, without issue.
There's no question in my mind that the combination of biomedia and plants really helps the filtration. Of course, the tank on the floor next to the air tank isn't necessarily pretty, but mine's in my basement where function is more important than form.