I should admit this first: I've wanted the St. Louis Cardinals to sign Zack Greinke since back when he wanted to retire and play golf professionally. Since then he's had one of the best seasons of the last decade, been traded for a bunch of not-quite-elite pieces, and, having failed to bring the Milwaukee Brewers to the World Series in the two years he was under team control, started to come up in trade rumors again. The Cardinals need a starting pitcher—especially if Chris Carpenter remains injured—and, wouldn't you know it, Zack Greinke is a starting pitcher.
The cost in prospects would be high, but the Cardinals have enough to cover it without completely obliterating their system. The wrench in the works: What do you do with Zack Greinke afterward? He's going to want $100 million, and I'm not sure the Cardinals are going to want to give it to him. That very ambivalence about committing to a pitcher who's failed to establish himself as a star or a disappointment is exactly what's put him on the market in the first place.