With all respect to Alan Alda, who was wonderful in the role, imagine Bob as Senator Arnie Vinick in the last couple of seasons of "The West Wing."
And, while I can't think of a specific character he should have played, I'd have loved to have seen him in Joss Whedon's series "Firefly." Whedon came up with a wonderful kind of use of language for that series, and I think Bob Culp could have hit that very descriptive and literary dialogue out of the park.