You could add a couple Blue Acaras. I don't know but I just have a thing for them. They are one of the calmer types of cichlids. You can see a pic of the ones I have by looking at the pic to the left. Try to get a male/female pair if you can. Also they are easier to breed if that is what your looking for. They grow to about 7" or so when adult.
In my 125 gallon i have 2 fully grown Male Sevrums, An adult Male green Terror, and an adult Female Blood Parott. All get a long just fine. Never have any problems.