Thanks for all the help guys. Sorry I haven't had time to reply sooner.
The good news is my friend is taking a very serious approach to this, and is committed to doing this the right way. I've given him several fish books, including a very good saltwater book (so he can see for himself the extra care involved). He's open to suggestions and is in no rush to just toss some fish in. He wants to first learn as much as possible. If only more fish keepers were that way.
The bad news is his tank is not a 20 long, its just a regular ol 24" x 12" x 16"?
Oh well, now what? We'll see, maybe after doing some of his own research he'll try to come up with bigger tank.
On the other side of the spectrum I have another, and much younger, and more eager friend (14) who just received a 29g from his grandmother. I suggested that a pair of convicts or perhaps firemouths would be a good first cichlid/real fish experience. He prefers the firemouth, I just wanted to see if you agree/disagree that a pair would be suitable for a 29g?