I have two golden algae eaters, they are incredible. I put one in my empty 4 gallon to clean and it was spotless in one night. The thing is, they grow to about 6 inches and sometimes even bigger which no1 told me and they can turn aggressive, I have had mine for about 2 months now and I haven't had a problem, they seem very timid and like to hide under my driftwood, they work better at night IME and act very skittish in the day. IMO these are way better than a pleco but you just need adequate room.
Another algae eater you could get would be an oto or depending on the size of your tank possibly 3 or more.
The fish someone posted looks to my like a SAE or flying fox, I have a flying fox but they don't do very much at all.
what i want is a fish that will not be nipped at or bother a betta. and that not even an oscar has interest in.