If we ever get some good Marvel cartoons again, I'd love it if Kevin would lend his talents to a few characters. As to who he could give voice to:
I wouldn't have said this a few years ago, but Captain America. Cap is a much more grim hero post 9/11, and Kevin's voice would portray the man Steve Rogers is now perfectly, bridging the gap to the tired old warrior he will (possibly) become in Earth-X.
I think The Punisher would be too dark for Kevin.
In sticking with the millionaire playboy characters, there's always Tony Stark. Although Tony's voice was never that intimidating out of costume, but imagine Kevin's voice with the Ironman robotic filter effect. Avengers Assemble!