I might get more excited about the winter meetings than any other time of year. My frequent lobbies for press credentials so far haven't been answered, but I can hold out hope. As for your Houston Astros, you can hope for big names to come walk through the door, but it just isn't going to happen this year. Still, there are a few names out there that can make 2012 a little more bearable.
Instead of breaking this down through ranking, we are going to split it up by need. The most pressing need in terms of current need is probably behind the plate. The Astros have Jason Castro returning from injury. Otherwise, they have three or four catchers (if you count Craig Tatum) that combined to be the worst-hitting catchers in baseball last season.
Humberto Quintero is a solid backup catcher, but he should not be playing regularly. So, the Astros could sign a veteran that is capable of playing half the time in order to prevent him from taking on 300 or more plate appearances. If Castro can play that player would platoon with him in addition to pinch-hitting or playing some first base.
After that, the club could use an additional relief pitcher for depth. Mark Melancon is a decent closer, but probably more suited to setup. Brandon Lyon may return from injury. The rest of the bullpen is young and relatively unproven. Another veteran to throw in the seventh or eighth inning would help.
The rest of the free agents are all dependent on what happens in the offseason. If Clint Barmes leaves via free agency then the club will have to address the hole. If they trade Wandy Rodriguez and/or Brett Myers then they will need to address the end of the rotation as well.