Jason Heyward- At one point was on pace for 45 HR and 135 RBI. Injuries have bothered him since but still has a great future ahead of him
Stephen Strasburg- Leads baseball with over 12 K/IP
Johnny Venters- 95mph fastball, 95mph sinker. Makes hitters look silly
Buster Posey: Could be the third best catcher in baseball behind Mauer and Brian McCann.
Jeremy Hellickson: 3-0 sub-2 ERA.
I know I'm leaving some out but those are some I have noticed.
The obvious names have been named. Posey, Jackson, Davis, Strasburg, and Heyward. Neftali Feliz should probably get more recognition for what he's done in Texas, but I'd also like to throw Starlin Casto into the mix. It's going to be really close for Castro, but it looks like he MIGHT have enough at bats by game 162 to qualify for the batting title. He's at like .315 right now, and if he continues to hit, and gets 502 plate apperance he might win ROY. IMO, Castro, Posey and Jason Heyward are going to have the best careers out of the rookies this season.
Also, Jaime Garcia. Nobody has named him, and he's been fantastic.