The Texans traded their 51st pick to the Minnesota Vikings, who in turn selected Stanford running back Toby Gerhart.
There are sure to be a lot of people who thought the Texans should have drafted Gerhart, the 2009 Heisman Trophy runner-up, but it's obvoius that they would have taken him there if they wanted him and felt he was the right value.
That was the Texans' 10th draft-day trade in history. They acquired the 62nd pick (second round) and 93rd pick (third round) in the move. They now have two picks in the third round, 81st and 93rd.
(UPDATE (6:56 p.m.): Here's a little more on the trade.)