Here is a list of 5 top prospects that should come up to their major league team's this year and make an impact. These kids have great value moving forward in keeper and dynasty leagues.
1. Trevor Bauer ARI
I think he comes up at the All Star break and will have a K/9 rating over 10. Bauer has 76 strikeouts in 61.1 minor league innings.
2. Anthony Rizzo CHC
Struggled a bit when he was up in San Diego. The Cubs have announced Bryan LaHair would move to the outfield to make room at first, it's only a matter of time before Rizzo gets the call.
3. Wil Myers KC
Possibly the best outfielder in the minors right now. He has better minor league statistics than Bryce Harper.
4. Travis D'Arnaud TOR
The eventual replacement for J.P. Arrencibia behind the plate is currently hitting .307 with 10 home runs in 50 games in the Pacific Coast League.
5. Yasmani Grandal SD
Nick Hundley is struggling and the Padres need to get their young guns to the bigs soon. Alonso is already up.
Keep in mind that these guys are not my top 5 prospects but they are, in my opinion, the 5 guys that will have the some of the biggest fantasy impact in 2012.
Some long term prospects I like:
Manny Machado BAL
Bubba Starling KC
Nolan Arenado COL
Miguel Sano MIN
Jacob Turner DET
Jameson Taillon PIT
Gerrit Cole PIT