20Gal High HELP!

I have a 20g tank with just a pair of Yellow Convict Cichlids. Tank is a 20g high, small whisper power filter, bubblewand, and heater.

For a 20g high i suggest a pair of convict cichlids, or a pair of rams, or a pair of apisto's. Can't really do much with a 20g high when it comes to cichlids.

For a 20H I would filter it with a Aquaclear 200 and a corrner sponge filter (dirt magnet). A good quality100W submergible heater will be needed.
While the tank is cycling you can find which cichlid you really want or maybe have your LFS get something uncommon. A few idea would be Rams, Laetacara dorsigerus or curviceps, Herotilapia multispinosa (rainbow cichlid), Keyholes, Cryptoheros nanoluteus, Cyptoheros sp. Honduran red points, Apistos, Basically any cichlid that doesnt get more than 4.5"-5" for a male if you want a pair. If you want a small community you could have a ram, a keyhole and a curviceps, I would stay away from Cryptoheros for a community tank.
I dont know alot about Africans but you could get some kribs (Pelvicachromis sp.), Tanganyika shell dwellers, or lionheads.
Just make sure your tank is ready and has the correct parameters ( some speices are more delicate than others)
Keep us updated with your progress and choices

depends on the kind you keep. South/Central Americans, like rams, would like driftwood, some rocks, and plants. Tanganyikan shelldwellers would want nothing but rockwork (I would to the shellies - very cool little fish).

Bolivian rams are a great choice! They are usually long lived and peaceful community fish. The corys would be ok, but don't add them until your tank is about three months old. They need a well conditioned tank. The danios are a very busy fish and might bother the rams. You could go with some tetras as these guys will not bother the rams near as much.