As someone else said, the names in this thread shouldn't be considered likely to make this type of leap in production, just potentially capable. With that in mind...
Bradon Allen/Chris Carter: Both find themselves embroiled in a battle for at-bats at 1B and DH with Daric Barton and Kila Ka'aihue. Both have excellent raw power, and both have contact issues. If either, or both, run away with regular playing time they could be sources of power. Of course, they'll need to strike out less frequently for that to happen. The A's are rebuilding, so they may get some leash. Kila Ka'aihue is out of options, so he may have a slight leg up in the competition. I've also seen it floated around the net that the A's are shopping Allen, so perhaps his chance will come outside of Oakland... or not at all.
Mat Gamel: Ugly strikeout rate in the majors, but under 20% at Triple-A the last two seasons. He's always gotten good scouting reports on the bat, the glove is another story. He looks to be the leader in the club house to replace Prince Fielder at 1B for the Brewers, so opportunity is there. He had his best home run output last year, 28 in 545 plate appearances. Granted, that came in the hitter friendly PCL. There was a time people were excited about him as a prospect, perhaps he begins living up to those expectations this year.