Frank also did the Dark Knight Returns stuff.
I'd also recommend Joss Wheaton (he did Astonishing Xmen for the first year), Judd Winnick, and Gail Simone (who also plays city of hero's in the Pinnacle RP Congress if you care about that game)
Almost forgot Mark Waid (JLA year One), Bindis (Currently doing new avengers, and Ultimate Spiderman), Kurt Busheik(Marvels, Liberty Project, and Conan are His comics), and Troy Hickman (Common Grounds, and He did some work on City of Hero's own comic which you can pick up in PDF format at the website.)