your tank is quite large so with good filtration and a understanding of the fish I would be happy to keep a few smaller plecos in the tank.
Myself I would avoid any of the larger plecos as this may result in a bio crash due to the waste even with lots of water changes.
You could try some of the larger Whip Tails as they would not produce waste in large amounts
A trio of the following could look good and they tend to be out and about a lot
http://www.planetcatfish.com/catelog/species.php?species_id=77
http://www.planetcatfish.com/catelog/species.php?species_id=405
maybe a few a small group would look nice
http://www.planetcatfish.com/catelog/species.php?species_id=722
Any of the group Hoplosternum or Dianema they are nice in groups and they do keep the substrate turned over with the constant grubbing around on the bottom. Also these fish would ensure that very little waste food was left to build up.
Some of the smaller Pims also ie Pimelodus pictus or Pimelodus ornatus both are fish that are happy in small groups of 5 or less. Again they would deal with the waste problems and are great diggers.