Hiya,
I would advice AGAINST convicts as they will beat up the most agressive of cichlids when breeding, which is all the time Lol.
Cant really suggest many good tanks mates even with that sized tank. I have kept angel fish with a pair in a 40gallon tank with no worries but it might be a one off thing. If they where to fight the angels would get a beating.
Some of the smaller geo species would deffinatly work. But it depends on the size of your tank ... if its 4ft x 18inches or similar then I would go for a small shoal (3) geos. They may outgrow the tank in time but it is possible.
Joel