Just found this little app, i dunno if it has been posted before, but i have just downloaded it and it is excellent. Shows your friends list like msn messenger, you can send messages direct from it, receive them etc. Also gives some neat breakdowns of your friends gamerpoints and stuff.
If you use XBL and have a mac, then get d/ling
http://mindquirk.com/xlf/
If you use XBL and have a mac, then get d/ling
http://mindquirk.com/xlf/