Nobody is going to cover this in the wake of the big trade today, but the Mariners have come to terms with second round pick Rich Poythress. I haven't found any reports of how big the signing bonus is. Poythress was the M's pick between Steven Baron and Kyle Seager, both of whom have already signed. Seager is in Clinton right now and doing more than fine. It would not surprise me if Poythress also begins his pro career there.
Poythress was on my 2009 watchlist. He's got some serious power in his bat. He played third in college but most everyone believes he will end up at first base. His bat is what makes him a prospect anyway, so it's not a big deal if he has to switch.
UPDATE (4:35 pm PDT) - Poythress will start his career in AA according to reports. The M's must like his bat even more than I do.