He's said he won't play until at least June, if at all. Now that the Astros can negotiate, there's 3 teams with a real shot at signing him for the rest of the year (sorry, Texas Rangers). Here's how I see it for each team, pros and cons.
Boston Red Sox:
Pros--Will offer him a ton of money, with a real chance to win. A playoff rotation of Schilling, Beckett, Clemens, and Wakefield would be TOUGH to beat. Lineup will score a bunch of runs for him every time out. Can end his career where he started it.
Cons--I don't really think anybody knows how he feels about the way things ended there before. It could be not as bad as some think, it could be worse. Uprooting for a summer when you've been retired for 6 months and playing 2000 miles from home might not be that appealing.
Pros--They can offer him 3 things that the other two teams cannot. He can stay at home, and pitch at a ballpark that is 20 minutes from his house. They will almost certainly give him the same arrangement he had before, where he wouldn't be required to travel on road trips which he isn't scheduled to pitch. And there's the distinct possibility that his son will be a September callup when rosters expand. The idea of playing a couple of games in the bigs with his kid has to be appealing. Houston has a chance to contend as well.
Cons--They won't be able to offer what New York and Boston can. The Astros have to hope that the $100+ million he's earned in his life is enough, and his decision will not be just about money. They will start out offering $18 mil pro-rated ($3 million a month, which for June through Sept. would be 12 mil), and would likely go a little higher, but not much.
New York Yankees:
Pros--They'll be willing to pay anything he asks, given the shape their staff is in. If he asks for $25 million for the rest of the season, I doubt they'll blink. He has a lot of friends there still, he's very close with Jeter, Posada, and Joe Torre. The Yankees will also score a TON, there's no chance he gets shut out in half his starts again. With their lineup, he could come back in June and win 15-17 games.
Cons--He was upset about New York giving up on Andy Pettitte and not offering him a contract after the '03 season, but I doubt that would factor into his decision much. But it would be another big move, just when he's settling into retired life with his family.
In summation, I think Houston has the best shot, for 5 reasons.
He and his family already live there, as stated above.
The travel arrangement, as stated above.
Possibly playing with his son, as stated above.
Can join a contending club and try for another playoff run with his hometown buddy, Andy Pettitte.
I'm a homer, and I refuse to envision him in another uniform this year.