The Boston Herald's Mark Murphy is reporting that the Celtics have signed 38-year-old power forward P.J. Brown.  Said Brown of his return to the NBA:

I'm just trying to make a dream come true.  I feel like this is one thing missing from my career. Boston has been coming after me pretty much the whole year. I thought one thing that kept the door open was coming back to win a championship. This team has a great chance to do that.

The 6' 11" forward made a name for himself thanks to his tough defense and above average rebounding.
Brown adds much needed depth down low and perhaps most importantly, he brings with him an immeasurably important veteran presence.  I mean the guy's played in 81 playoff games in his career!  He also instantly becomes one of the best big men on the team in being able to hit that 15 to 17 footer from outside the paint.  And on top of all that, he's been regarded as one of the more considerate and courteous players in the game for years.  Brown last played for the Bulls during the 2006-07 season and has spent time with the Hornets, Heat, and Nets during his 14 year career.