Sorry guys, all the Planted Tank hosted pictures disappeared, I looked at my harddrive and couldn't find it right away. I'll keep looking and re-post them if I find it.
Basically it was just a powerhead, turned upside down, with a sponge stuck to the inlet. I used one of
these sponges, cut them into quarters (like a cake), cut a slit in the center and stuck them on the powerhead, using an inlet strainer to stabilize that thing.
The AC30 powerhead and the sponge is still the only filtration on my 36 gal tank, and while I have been considering to replace it with a canister filter to get some equipment out of the tank (filter and heater and CO2) it works extremely well. All I do is pull the sponge out every 4 weeks or so and give it a good squeeze in a bucket.