No word on who other than to say it's not Tommy Hanson. Will update as updates come.
UPDATE: I've got names: Charlie Morton, Gorkys Hernandez, and Jeff Locke. And Andrew McCutchen gets the call to Pittsburgh.
UPDATE #2 (aka, the long update): John Sickels had Hernandez and Locke both graded as B-'s before the season started, which would approximately place them around Bryan Morris-level prospects. Locke was a second round pick in 2006 right out of high school and he's still very young. His record was ugly last year, but his peripherals were very nice for a 20-year-old playing in low-A ball. Being a young left-handed starter with a big arm and huge upside, I'm betting he's the player Huntington was after in this deal.
Hernandez is an interesting prospect in the Jose Tabata mold. He was signed by the Tigers out of Venezuela and sent to Atlanta in the Jair Jurrjens/Edgar Renteria trade. He's been pretty aggressively pushed through the minors, as he's in AA at the age of 21, and his numbers are pretty good considering his age at each level. The Tigers and then the Braves were both waiting for him to flash some more power, but he's a great athlete, fast, and good defensively according to this profile, so the Pirates are possibly hoping he'll develop somewhere along the Andrew McCutchen curve.
Morton might be plugged into the rotation right away. He's 25 and he's put up great numbers in the International League in the past two seasons. This Scout.com profile describes him as an "enigma" with great stuff that's a bit of a head case. He made 15 not-so-good starts with the Braves last year, but like I said, he seemed to take a step forward in AAA last year and isn't terribly old. He sort of fills the same role that acquiring Karstens, Ohlendorf, and McCutchen did last year, he provides immediate pitching depth that with some coaching could potentially turn out to be something a little more.
I'll write a longer post with some more opinion in it later tonight.