Reimold is already up. Beckham and McCutcheon are the only two who have a chance this year, Alvarez and Smoak have a while yet. Beckham shouldn't be called up, so realistically, REimold and McCutcheon are the only two.
Smoak wouldn't do better than Helton right now, you'd be better off with Helton.
As for pitchers, if no one has heard of Medlen, then I'll have a long list. For Medlen, everything is speculation. If he pitches well enough he will stay in the rotation.
Feldman, Cecil, are already called up but are good choices. Purcey and Niese have been called up already but currently are in AAA, and David Huff is also in AAA. Those guys are just off my team, I'm sure there are plenty more.