I like the Executive Defender from Surefire. It's very similar to other Surefire's except it's got bezeled edges on either side for self-defense. I always bring it to the bathroom when I go, just in case. I've heard a rumor though that you can't bring them through security anymore. I haven't had any problems though.
http://www.surefire.com/maxexp/main/co_disp/displ/prrfnbr/1132/sesent/00
http://www.surefire.com/maxexp/main/co_disp/displ/prrfnbr/1132/sesent/00