Adrian Gonzalez is an obvious choice. But seriously, and this may seem extremely bias coming from a Giants fan, but I honestly think Pablo Sandoval is the most under-rated player in baseball. His downside is that he is pretty damn slow around the bases, and with the way the Giants have put him on defense he has been taken out of his natural position (catcher), but I honestly think this kid has it all. We have molina, and with Pablo's upside it is a necessity to make him an every day player- he is too slow to play third (though he has a solid arm) and if not catcher his only real option is 1st (but he is a bit short). Really though, in 41 games last season he hit .345, that being his first season, and he's currently hitting .325. Someone prove me wrong, please.
My other choice is Ryan Zimmerman. He is playing for the worst team in baseball, which might make him stand out a little more, but I really wonder where the team would be without him.