I just have a common pleco in there currently and he does wonderful, and I am growing out a rubber lip pleco to go in there, now he's too small and they pick at him when he was in there. Basically anything that will stand up for itself against them.
I keep Bristlenose Plecos with my Malawis. They seem to do well. They have even bred a couple of times over the years, but I think the cichlids have eaten most of the babies.