From what I have read, My best guess would be no earlier than June 1st and the Yankees and Red Sox would be the most likely candidates.
I would say the Yanks are the front runners as they will be able to offer the most as a prevoius posting had stated that they are in the most desperate shape for pitching and have Pettite (Clems best friend).
However, do not count out the appeal for Clemens to end it where he started it...Boston and right a wrong that Dan " Roboto" Duquette ( "twilight if his career";"more days in first place" ) made.
Additionally, Clemens is well aware of his place in history and with other active pitchers trailing his wins and K totals by only a few ( e.g., Johnson), he would want to gain some seperation by coming back to a team that would be able to win.
Johnson 280 wins 4544 ks
Clemens 348 wins 4604ks
Maddux 334 wins 3179 ks (not close) - wins the factor here.
P.S. One big factor not to overlook would be the attraction to play with his son who, I believe is in the Astros system. However, as history has shown he would not in all liklihood get a lot of wins from Houston.
1. Yanks 45%
2. Sox 40%
3. Astros 15%
Pulled these out of thin air of course, but my best guess.