Obama ought to grab hold of Bill Richardson-it would help secure that Hispanic vote which Hillary claims Obama is unable to get on his own.
Clinton would do well to take Ed Rendell (Pennsylvania Governor), he is a strong supporter of her and although I don't believe half the rubbish flowing from his lips, he has a way of convincing people that he's really looking out for your best interests (much like Clinton does).
McCain might do well if he brought in Mike Huckabee. Huckabee would bring in some of those Conservatives who are unsure of McCain.
According to this (which has already eliminated Clinton from the running):
Exclusive Poll: Ed Rendell Strong V.P. Candidate - Local News Story - WCAU | P the following has been found-
McCain-Huckabee vs. Obama-John Edwards: Obama, 50 percent; McCain 40 percent.
McCain-Huckabee vs. Obama-Kansas Gov. Kathleen Sebelius: McCain, 45 percent; Obama 42.
McCain-Huckabee vs. Obama-Rendell: Obama, 47 percent; McCain 40 percent.
McCain-Huckabee vs. Obama-Sen. Chuck Hagel (D-Neb.): McCain, 42 percent; Obama 40 percent.
McCain-former Massachusetts Gov. and presidential candidate Mitt Romney vs. Obama-Edwards: Obama, 52 percent; McCain 37 percent.
McCain-Romney vs. Obama-Sebelius: McCain, 41 percent; Obama, 40 percent.
McCain-Romney vs. Obama-Rendell: Obama, 48 percent; McCain, 39 percent.
McCain-Romney vs. Obama-Hagel: Obama, 42 percent; McCain, 41 percent.
McCain-Minnesota Gov. Tim Pawlenty vs. Obama-Edwards: Obama, 52 percent; McCain, 35 percent.
McCain-Pawlenty vs. Obama-Sebelius: Obama, 41 percent; McCain, 38 percent.
McCain-Pawlenty vs. Obama-Rendell: Obama, 49 percent; McCain, 37 percent.
McCain-Pawlenty vs. Obama-Hagel: Obama, 42 percent; McCain, 36 percent.
McCain-Sen. Joe Lieberman (ID-Conn.) vs. Obama-Edwards: Obama, 50 percent; McCain 38 percent.
McCain-Lieberman vs. Obama-Sebelius: Obama, 42 percent; McCain, 41 percent.
McCain-Lieberman vs. Obama-Rendell: Obama, 48 percent; McCain, 39 percent.
McCain-Lieberman vs. Obama-Hagel: McCain 41 percent; Obama 40 percent