If he proves he's healthy until the trade deadline Morneau would bring back a better return than many people are predicting here. John listed the Pirates, Blue Jays, Marlins, Indians and Mets as possible suitors and others in this thread have mentioned the Cardinals, Rangers, Phillies and I'd throw in the Dodgers with their new ownership, poor 1B play and division lead.
It's all about supply and demand. There is a ton of demand for a power hitting firstbaseman and very little supply. If multiple teams are interested, odds are the Twins are going to get a fantastic offer from one of them. If he can show he can stay healthy, he is definately a player that could put a contending team over the hump, and that is what teams are actually paying for.