Remember the official StR Ike Diogu/Leon Powe comparison post? Sean May would fit into that. If he fits into anyth-- no, I'm not going to head down that road. We don't need this post to be 5,000 words.
All three power forwards have put up similar NBA numbers.
May has the advantage of being one year younger than the others, and of being the best defensive rebounder of the bunch. (He has roughly the same career defensive rebound rate as Spencer Hawes, slightly better than that of Jason Thompson.) But he's not as efficient a scorer as Powe, nor is he as potent as Diogu.
This is all to point out that there seems to be little advantage to taking May instead of Diogu unless Diogu is asking for more than the minimum or you have a hunch May's going to improve rapidly once he gets on the floor in a new situation. (That's not a far-fetched hunch. It's a bit hopeful, sure. But young players do improve, and May has only played 1,500 minutes -- the equivalent of a backup point guard's minutes -- for his whole career.) Further, there's really no reason to pay May or Diogu more than the minimum, assuming the other (the second choice) is available for the minimum.
(And once again, consider this an endorsement of Powe. Feel free to sign one of these other dudes, but strongly consider Leon now or when his knee is right. He's more than a charity case. He's an incredible weapon off the bench.)
By the way, the minimum contract for each of May and Diogu would be $884,881. Because of a somewhat bizarre rule in the CBA, the league reimburses teams for a portion of salary paid to minimum-salary players (in order to boost the prospects of veterans, whose minimum salary can reach above $1 million). So May or Diogu on a minimum contract would only actually cost the Kings $736,420 according to Larry Coon, although each would pull in $884,881.