Any monologue can have humor in it. So many actors make the mistake of choosing pieces that are "funny" and they fall flat on their face because they deliver them as if they are "funny."
I suggest you can find humor in anything. And to do a "serious" piece and make people laugh is a bigger challenge and therefore more rewarding because they will never have seen the piece done in that way.
i saw a Richard III that had the audience laughing almost to the end.
If he could have pulled it off, I'd love to have seen Jerry Seinfeld (or someone like that) do Hamlet.