VP on the Dem. side? I'd say Martin O'Malley probably tops the short list. I've also heard Elizabeth Warren's name mentioned, and Sherrod Brown.
On the GOP side, I think someone will be hard to find. The accusations and name calling run pretty deep, and the hatred that some of these guys have for each other is too obvious. Someone who was in the field early, like Jindahl or Graham, might make it. Maybe Trump could get some help with his wall by picking Maricopa County Sheriff Joe Arpaio.