President and co-founder of Cressey Performance, based in Boston, Eric Cressey has quickly become the go-to guy for baseball-specific training. Whether you want to develop a workout program as a pitcher, or you simply want to find some effective rotator cuff exercises, this should be the first place you go.
Steven Ellis is a former Cubs pitcher who is best known for his book 'TuffCuff,' which is an excellent resource for developing a workout program for young pitchers.
Even if you choose not to purchase his book, there is a plethora of information on his website, and the forum is particularly informative if you can sift through the nonsense.
Offering a rather unique philosophy on baseball player training, and with a number of accomplished pro pitchers vouching for them (e.g., Clayton Kershaw, Cole Hamels, Barry Zito), they've got to be included in the conversation. Most recently, you might have heard them mentioned in the discussions of up-and-coming pitcher, Trevor Bauer, who swears by the program (see here: http://sportsillustrated.cnn.com/2012/writers/albert_chen/05/07/dylan.bundy.trevor.bauer.long.toss/index.html).
While purchasing Pourciau's Top Velocity program is quite expensive, and Brent's site is a little too 'in your face' for my liking, there is a lot of good information here, and like Steven Ellis' site, you can greatly benefit just from participating in the forums.
I also hesitate to put Paul on this list, largely for the same reasons as Brent - he's quite gimmicky, and his overzealous marketing can be quite annoying (if you subscribe to his e-mail list, prepare yourself, as he will bombard your inbox). He undoubtely gives off the 'snake oil salesman' impression.
With that said, however, he actually does know what he's talking about, and even if you simply watch his Youtube videos, I suspect you'll find a lot of information that will help you out.
select one here...