Several things strike me about the June free agency situation.
1. The Celtics will have seven unrestricted free agents this June. Pierce also has a player option and could in theory opt out, although I doubt he will. There will be significant roster changes in Boston whether or not Ray Allen is traded before the deadline.
2. Everyone is talking about the top end free agents, e.g. Joe Johnson, LeBron James (player option), Chris Bosh (player option), Dwayne Wade (player option), Manu Ginobili (although I can't imagine him leaving San Antonio), Carlos Boozer, Amare Stoudamire (player option) and Michael Redd (player option).
But there are quite a few good players who will be unrestricted free agents and who might be available for the MLE or less. The following names caught my eye as potential targets for the Celtics: Acie Law, Travis Diener, Udonis Haslem, Chris Duhon, Al Harrington, Louis Amundson, Steve Blake, Travis Outlaw, Nate Robinson, Kyle Korver and Brendan Haywood.
3. There are also players who will command more than the MLE but who might be available in a sign and trade, e.g. David Lee.