Yep aquaclears are the reigning king of HOB filters, arguably they're the best filter period... relatively cheap, space for biomedia and they last forever. Furthermore they have adjustable flow, and the intake is easy to cover if you're worried about small fishies getting sucked up. The HOB format is nice because although there are lots of awesome sponge filters and internal filters out there, those two types do take up space in the tanks and don't add anything to the aesthetic point of the tank!
I would recommend an AC20 for anything 40L and under while you will want an AC30 for anything 100L and under.
Eheim has a few good lines too, but they are decidedly pricier. I am also very happy with my Fluval Plus line (being replaced by the Fluval U line). I have the 1+, 2+ and the 4+ but again, as internal filters they do take a lot of effort to conceal.
Just whatever you do don't get rooked into any HOB filter (ie Tetra Whispers) where you have to purchase those special carbon filter inserts. They are terrible media and the whole idea is pretty much a money grab for the manufacturers to guarentee you'll pay them $5 a month for filter inserts for the rest of the life of the filter.