Everyone in the fantasy community knows about David Price and Matt Wieters.
Here is a list of players that are just as exciting as those two, and may be getting a call-up soon.
Tommy Hanson(SP, ATL)
Hanson has been dominant thus far at the Triple-A level. Through six starts, he has posted a record of 1-3, with a 1.65 ERA. He has also fanned 48 batters in 32.2 innings of work.
I expect Hanson to be called up soon, since Keshin Kawakami and Jo-Jo Reyes aren't getting the job done. Another obstacle in the way of his call-up is the status of Tom Glavine.
If Glavine returns and either Kawakami or Reyes get their stuff together, then Hanson could be waiting a bit longer to get to the big league level. So expect him to fill the fourth or fifth spot in the rotation when promoted.
Expect Hanson to be an immediate boost to any fantasy team's pitching staff.
If he is available in your league, I recommend picking Hanson up as soon as possible.
ETA: late May or early June
Mat Gamel (3B, MIL)
Gamel is one of the best power hitters on the Triple-A level. Through 25 games, he has a .356 BA with 7 HR, 28 RBI and a .700% slugging.
The only player standing in his way is the inconsistent Bill Hall. It is only a matter of time until the Brewers have to promote him.
Expect instant power numbers from Gamel at the big league level, in that high octane offense.
I don't think he will be called up for at least a month, so just put him on your watch list and check up on him periodically.
ETA: mid June or early July
Chris Tillman(SP, BAL)
Tillman is having himself a great season at the Triple-A level. Through five starts, he has posted a record of 3-0, with a 2.52 ERA. He is also averaging just a bit over one strikeout per nine innings pitched, with 27 strikeouts in 25 innings pitched.
The Baltimore pitching staff has been getting hammered through the first month of the season. This may lead to a call-up in the near future.
Tillman will likely replace Adam Eaton, who has posted a record of 1-3 in five starts, with a 7.18 ERA so far this season.
Expect Tillman to be an immediate help to Baltimore's pitching staff, when promoted. But like the rest of their pitching staff, he will probably give up a lot of runs.
I think Tillman is worth a roster spot on your team, especially if you are in a dynasty format league. He is going to be the ace of that pitching staff within no time.
ETA: early June
Andrew McCutchen (OF, PIT)
So far this season, McCutchen is off to a shaky start at the Triple-A level. Through 25 games, he has a .255 BA with 1 HR, 7 RBI, 5 SB and 20 R.
McCutchen was one of the leagues top prospects coming into this season, and almost made the 25-man roster at the end of spring training.
Even though his numbers aren't that good, Brandon Moss's are even worse. Moss is batting under the Mendoza Line one month into the season.
I don't expect Pittsburgh to let McCutchen sit in Triple-A much longer, now that they are starting slip to the bottom of the NL Central.
If you have a roster spot, I would pick up McCutchen now and stash him away until his promotion. He should instantly increase your runs scored and stolen bases once he is playing every day.
ETA: early June to mid June