Without a doubt, C Lee's walk-off grand slam in 2001 to finish off the Assholes on Addison in 10. Remember, that game was started by D Wells and the sCrUBS scored 3 times in the first and not a run after that.
A close second would be PK's 2 HR game after the Sox were losing 8-0 after 2 in 2002.
But there is nothing quite like a walk-off. Jose's was sweet but if JM knew how to handle a BP, the Sox never would have been in that situation in the first place in 2003.