Most livebearers are algae eaters, though I'm not saying they're all good at it. The "big four" definitely eat algae, even if not to the level of the Florida Flagfish, SAE, etc.
actually, have to agree. Goodeids are excelent algae eaters and are qquite good at keeping BBA at bay along with an SAE or two. My mollies now, they don't touch the BBA but they do eat the green that hangs to the back of the tank. I see them "kissing" it all the time.