Actually, many of the Mbuna cichlid species are algae eaters and are recommended for algae control in a cichlid tank, although I wouldn't think they'd keep your glass clean.
Some of the Synodontis catfish (which include the cuckoo catfish as HairyFish noted), would fit, but I haven't heard of them as being very good cleaners.
The big Plecos (common, snow king, sailfin) can go with cichlids and are good algae-eaters but will get too big for 29 gal. The Bristlenose Pleco can be kept with cichlids but stays small (6") and is a very good algae-eater.