:P How about James Earl Jones or Morgan Freeman?

If cost is an issue this guy may save you a few pennies
https://www.youtube.com/user/HOCgaming

John St. John (voice of Duke Nukem): http://www.jon4voice.com/
Few years ago he was selling his voice for $1/word. Might still be doing it.

Clearly we need to get Gilbert Gottfried on this.

I know this may sound daft but I'd love to have a voice acting role even if it was extremely minor. I don't know how many voices will be in the game and if my voice would be suited (having an English accent).

As for others, it really depends on what mood/settings/atmosphere Casey/Molly Rocket is going for. As Pee-Wee Herman may not be good for a very serious character.