Hapimeses on 02 February 2011
Also, while I'm here, I'll answer the OP fully as it seems no one else has.
Each one of your team-mates starts with a single outfit. When you complete their loyalty mission, you unlock a second outfit that you can choose before you head off on a mission. Further, there are currently two outfit DLCs. One already released -- Pack 1 -- and a second due on February the 8th, 2011 -- Pack 2.
Pack 1 gives you an new outfit for Garrus, Jack, and Thane. Pack 2 gives you a new outfit for Miranda, Tali, and Grunt.
In all cases the alternative outfits are cosmetic only and do absolutely nothing bar change a newly outfitted character's appearance.
So, there you go.
