ESPN has a page set up for all the breaking rumors.
Yahoo is updating this article with rumors as they become available.
The biggest deal out there right now is Shaq maybe going to the Cavs, but it sounds like that is not going to happen. Portland is sending signals that they will stand pat (I'll believe it when I see it) and while Stoudamire is still out there, they might just be happy to keep him and keep scoring 140 points a night.
Other than the Nocioni rumor, I don't see anything to do with the Celtics yet. By the way, Chad Ford updated his rumor saying that the Celtics insist that they are not trading for Nocioni. I believe them. It never made much sense to me to begin with.