You can also look at the Seachem Tidal 75. Similar to the AC's, but the water flows out across the top of the tank a little further than with the AC. You do have to keep the water high, though or it will drop off just as with the AC.
I use one Tidal 75 on my 40B. The flow control on the Tidal is so much better than the AC, too. I never really noticed much difference on my AC filters. With the Tidal, you can slow it to almost nothing or full power as required for your fish or plants.
There is also a Tidal 55, if you wanted 2 filters, or a Tidal 110, comparable to the AC110. For my purposes, one Tidal 75 has been sufficient.