go here: http://1337pwn.gameriot.com/blogs/1337pwn-Applications/XBOX-Live-Friends-List-Widget-Version-25 what you can do is download a little app that tells which of your XBox friends are online and what games they're playing. there's a version for Mac, iphone, blackberry and Windows. It's very handy ... used it several times already to see if my buddy was online before I decided if I wanted to play. used it on my iphone and Mac with good success, although the direct link to the Mac widget from the apple website didn't work. Had to get the updated version.
I use 360Live for my iPhone and it's a great app. It will tell me who's on, when they were last on, their entire gamercard. I can compare my games with theirs and I can also send messages to my friends via XBL through it as well, and read messages sent or reply to friend requests. Best of all it's free.