I just wanted to boost this thread to share my experience with rhino plecos.
After reading this initial thread I decided to buy a couple on Aquabid and give them a try. Snails have done wonders in my smaller tanks but they quickly get eaten by certain cichlids as I found out the hard way. Bristlenose used to keep my discus tanks clean, but all the ones I currently have are spoiled on pellets and algae wafers so they refuse to touch algae.
Even though my tanks are well-filtered and I do frequent, large water changes, my water out of the tap already contains nitrates and phosphates, so algae has been a constant battle for me since I moved into this house. I have changed lighting, length of time with lights on, upped water changes, scrubbed and scrubbed and scrubbed... I wanted to build an algae scrubber but there's no room under the tank and I don't want that eyesore sitting out in plain view.
So as a last-ditch effort, I got the rhino plecos. In two days, one 4" rhino pleco has cleaned about 80% of the heavy algae build-up on the overflow boxes and back glass of my 210 gallon. I was in awe. The larger cichlids leave him alone, he hangs out under driftwood during the day, and then at lights out he goes to work. Within a week that tank will be spotless.
Now for the down-side, and most pleco keepers know this already. This guy is a pooping machine. The first day I turned on the lights, I almost gasped out loud when I saw the bottom of my tank. Long, black poop EVERYWHERE. It was in huge piles all over the sand. So for the last two days, I've been having to siphon out about 10 gallons of water a night to remove all the poop.
So I guess my suggestion is to try to figure out what's causing your algae problems and fix that first. But if you've tried everything and nothing's working, try out a rhino pleco (if you have a tank large enough for it). Just realize that it's going to add extra work in the form of water changes and siphoning. In my case, I do large water changes and daily tank maintenance anyway, so it's not really too much of a hassle. The beautiful, clean glass is worth it for me.