Hopefully a good contender or prospect, Chris Arreola would be a good fight for Haye. Haye KO Arreola in 2.
Peter would be a good choice but that would probably be too easy and he'd KO Peter so quick it'd scare the Klits off after their respective battles with the flab-man. Valuev would be my choice but as has been pointed out he won't take the fight and neither would Arreola. Therefore John Ruiz springs to mind, he'd take the fight because he has balls, and would arrive in shape and ready to go. If Haye fought Ruiz and KO'd him it'd make noise.....
Haye needs someone to keep his career ticking over, a fight with a big name who is past it. Someone like James Toney, who can also bring a couple of alphabet belts to the party too.
Ruiz or Arreola for me. Ruiz is a big name and, provided Haye wins, he could see himself force his way into a mandatory position with the WBA. We know the Klits love mandatories so there would be no excuse NOT to fight Haye. That said, knowing the WBA, the winner of Wlad-Chagaev will probably be the 'Super Special Fantastic Awesome Champion' and won't need to face mandated opposition. As for Arreola, I like the fight and I also think Haye wins after an absorbing, action-packed contest. Maskaev could be a good option for Haye, too. Whatever happens with regards to getting a Klitschko in the ring, I think Haye seriously does need a fight soon just to keep him ticking over and ensure his validity with the brothers.