Also, you might want to avoid getting a pleco. Common plecos grow far too big for your tank and produce a ton of waste, which will in turn lead to water quality issues which would have a VERY adverse effect on Rams, if that is what you choose. You could go with a bristle nose or rubber lipped, but even then, they would probably barge in and eat any eggs your rams produced.
I would suggest cories, though many people don't advocate keeping them with Rams because they both keep the same quarters (the lower third of the tank). As long as you provide an ample number of hiding spaces, cories should be fine. (I have 3 aenatus in my 29 with a pair of Bolivians and have had no problems. The Rams will occasionally heard the cories around, but they don't mind much, have full fins and barbells, and still cary on normally). Also, you could add some otos to cover algae control. (Again, I keep them with Rams and they are hardly noticed).