I think Rick Perry would be a good choice. Santorum may need help in the South, and Perry could help with organization and money. And he will help with Hispanic voters.
Susana Martinez might be a good pick, but she would have to be well vetted first.
Perry is an embarrassing gaffe machine who will never get out of Texas again, and whose epic fail of a presidential campaign was so bad that it put his day job in jeopardy. Also, the last thing Santorum (or Romney for that matter) needs is a VP who reminds people of Dubya or Palin, and Perry combines the worst characteristics of both.
Really, I'm not trying to be wise with this remark, but aren't most VPs gaffe machines?
And maybe that is by design to make the guy at the top of the ticket look good?
Look at either the VPs that were actually in office, or were just on a ticket in the last 40 years.
Quite a bunch of controversial characters.