Hot off the presses:
A preliminary agreement has been reached between the teams for Atlanta to receive Teixeira and left-handed reliever Ron Mahay from Texas for catcher Jarrod Saltalamacchia, minor league shortstop Elvis Andrus and two minor league pitchers.
The Fort-Worth Star Telegram, citing a Rangers source, is reporting that the two pitchers Texas will receive are 19-year-old right-hander Nestali Feliz and another pitcher to be determined.
I'll have more when we know more.
Update [2007-7-30 13:25:25 by gondeee]:
It looks like it will be Salty, Elvis, Harrison, and Feliz, though no report has confirmed all of these guys yet. Coming back to us is obviously Teixeira, along with Ron Mahay. Upon first blush I didn't like this trade, but I'm starting to warm up to it (a friend talked me into the benefits - I'll have more later)
Mark Teixeira's stats for your enjoyment:

Update [2007-7-30 14:11:51 by gondeee]:
Here is a great piece from Will Carroll at Baseball Prospectus that may put some Braves fan’s concerns about the trade to rest:
I spent much of last night trying to figure out if Matt Harrison was injured and thus out of the Mark Teixeira deal. Turns out that he is having some shoulder problems, and doesn't appear to be part of the final deal. It's this type of thing that makes this time of the year so interesting--imagine if Jon Daniels had pulled the trigger on the deal a day earlier and ended up with damaged goods. This type of pressure on Daniels and every GM has to be kept in mind--nobody wants a lemon, so everyone has homework to do. Criticism of Daniels around the league has been strong, but the level-headed John Schuerholz stuck to his task and got it done. There's little doubt that Mark Teixeira makes the Braves better, and it will be years before we know if the Rangers are better or if the cost was too high for the Braves.
Update [2007-7-30 16:6:20 by gondeee]:
The Mississippi Braves press release I just got stated that Matt Harrison has been placed on the 15-day disabled list, so I'm guessing he will NOT be a part of this trade.