While I trying to clear away the smoke coming from my computer since this trade became a reality around 6:00 p.m., I'll just add a couple of details that have been posted elsewhere. The deal isn't official with a capitol "O" yet, but it appears to be all but completed.
As previously mentioned, Miller, Maybin and Rabelo will go to Florida, along with reliever Eulogio De La Cruz (affectionately known here as "FuneralOnAShip"), and starting pitchers Dallas Trahern and Burke Badenhop. Basically, if you were a top pitching prospect for the Detroit Tigers, and you weren't drafted in 2007, you are probably now a Florida Marlin.
To answer a question posted in the comments, both Dontrelle Willis and Miguel Cabrera are eligible for salary arbitration for the next two years, and can't become free agents until after the 2009 season.
And if you ever doubted Jim Leyland was a cowboy, on a steel horse he rides, this whole thing apparently began when he went up to someone in the Marlins' front office and said, "We want Cabrera." That is awesome.
EDIT #2: Craig, the SB Nation Florida Marlins blogger at FishStripes responded in the comments and said Willis does indeed have two more years before becoming a free agent. You know, if the Tigers sign D-Train to a long-term contract, this will all be a moot point.