Blehhhh rams and kribs, thats all you hear mentioned these days. I dislike both personally....to common for my tastes. Most of the Dwarf Cichlids should be ok. And dwarfs don't just mean rams or kribs (kribs arn't even in the "dwarf" category..at least not on America's side of the world.) There are many many types of Apistogramma you could look into, or if you can find them....Checkerboard Cichlids (Dicrossus filamentosus).
The Checkerboards are probably the most peaceful of those mentioned in this thread. And they only grow to about 3".
As for the pleco, hit or miss. I've heard of Rams, kribs, apistos, etc all harassing plecos/loaches when they are spawning. But you should be ok keeping him and a pair of something together.
You do have another option that i might toss out there. It doesn't involve the pleco, but i'll throw it out anyway. Tanganyika Shelldwellers. They are very small, interesting fish that could live in a small tank like that.
