Upon reading the excellent miniseries 'Deadpool: Suicide Kings,' I thought the Cage the Elephant song "No Rest for the Wicked" made a good theme for Tombstone. The song is about how basically everyone is selfish and does any evil they deem necessary to survive, and Tombstone seems to hold to that view. The hideous things he does to others in that miniseries (Or, in the case of Conrad, threatens to do) were done mainly because he felt he had to do so to ensure that he'd get what was owed to him and preserve his reputation among the criminal underworld (Though of course, he obviously got a great deal of satisfaction from those actions, as well).
I could see dc Talk's song 'What if I Stumble?' as a good theme song for Patriot from the Young Avengers. I'm not sure if the song's religious nature works, as it's never been established what religious beliefs Patriot may have, but it seems from what I've read that Patriot is frequently concerned that his own failures will harm/ discredit his friends and teammates, tying perfectly into the song's refrain of, "What if I stumble, what if I fall? What if I lose my step and I make fools of us all? Will the love continue when my walk becomes a crawl? What if I stumble, and what if I fall?"
I might come up with some others later.