The most common fish to go with gren terrors are oscars, red devils, jaguars, and jack dempseys. But all of these fish can very greatly in agression levels. Its best to grow them together young. Introducing new fish when the current fish are full grown can be difficult.
A texas cichlid might be good too. However, the two that I bought both got hole in the head.
Of all the cichlids that I had (all the ones above), the red devils have been the most disease resistant. Maybe its just luck, but out of four red devils, none have died of disease. The oscar and texas cichlids quickly died of hole in the head after I got them. the jaguar cichlids have been disease resistant as well.