I've got a borneo sucker in my tank; I'm not sure whether they're related to catfish or not, as they only bear the slightest similarities to sucking species of them, and they use their entire bodies, which are shaped a bit like a marine skate or flat-bodied shark, to cling to the glass, somewhat like a snail. I find them to be incredibly good - they don't just remove algae, but also eat things like hydrai, which can quickly overrun tanks by settling on th undersides and sides of plants and aquarium objects like heaters and filters. They don't tend to travel on gravel, though - either you need large, smooth rocks for them to cling to in order to rid the bottom of algae, or they'll stay predominantly on the glass.