We've been having this discussion at SNKT, as well.
T-Mac said Suns, Rockets, Lakers, or Spurs.
As far as the Suns go, I've heard that the Suns would like to do Marion for McGrady straight up, but the Magic want Joe Johnson too.
Yao Ming aside, the Rockets would probably trade anyone for McGrady, but Francis and/or Mobley would have to be part of the deal.
Around the Horn has said the Spurs would have to give up Ginobili (who is a FA this summer...restricted I *think*) as part of any deal.
As for the Lakers, T-Mac for Kobe seems the only possible scenario.
I'll go get the article for you.