I think Chump is right that Floyd should be the one to go if we make a move. Cameron's value is at an all-time low, and Floyd's is on the rise. That being said, I don't know if I'd be in such a rush to make a move. Floyd and Cameron are both questionable health-wise, and Diaz is still somewhat of an unknown. He's putting up huge numbers, but it's only been a month, and this performance is pretty out of line with his minor league performance. I think he'll be a pretty good hitter, but I'm not 100% sold that he's going to be that good this year. I think I'd wait a little while to make a move. Once Cam comes back, work Diaz into the lineup a few days a week, which should help to keep Floyd and Cam healthy. If the Mets are going to win this year, considering Floyd's injury history, I think they need a pretty good 4th outfielder. Plus, this way, we'll get a little more time to see if Diaz is for real before we count on him to be the starter for the rest of the year.
As for Piazza, I think it's a little early to start thinking about making mid-season dumps considering that it's April and the Mets are a half game out.