Bay Area World Series

These players are on their teams 40 man roster and not yet been in the big leagues, which obviously means they are quite well thought of by their clubs (being on the 40 man means the player is protected from being selected by another club in the Rule V draft)...

Astros - OF Andrew Aplin

Mets - RHP Chris Flexen

Phillies - RHP Mark Appel, C Andrew Knapp

There are other players who are going to get a long look in spring training who could break camp with their team, but being on the 40 man is a good thing for these 4 players.  If another player, say O'Koyea Dickson of the Dodgers, were to force his way into MLB with a great spring (and it's possible), he'd have to be put onto the 40 man roster, which would mean the Dodgers would have to also take a player OFF the 40 man roster.

In any case, I'd guess, of the four listed above, Andrew Knapp would be the next one to reach MLB UPDATE: (I got this right!  Knapp made the Phillies out of spring training as their back-up catcher).  Catchers and pitchers are ALWAYS close to The Show.  At some point, health of course being important, the Phillies will also need/want to see what they have in Appel.  

Other players to keep an eye on this season and/or during spring training: Reds INF Alex Blandino, Dodgers OF O'Koyea Dickson, Astros 3B J.D. Davis, Angels RHP Drew Gagnon, Twins RHP Zack Jones, Cubs RHP Jordan Pries, Cardinals RHP Robby Rowland, Marlins RHP Tyler Bremer, Rockies RHP Matt Flemer, White Sox 1B Danny Hayes, Braves RHP David Peterson, Twins LHP David Hurlbut

Some of these listed players are non-roster spring training invitees.  Among these players, Davis is one to also watch, he has hit a lot of homers in the minor leagues.  Zack Jones has been a Rule V draftee before and if not for injuries, there is a chance he'd have already been up to MLB.