To accompany the recent Xbox 360 dashboard update, 1337pwn.com released a new version of their Xbox Live friends-management iPhone application. iNXES lets you view your friends list in the NXE form complete with avatars, gamer scores, and online status.
In my testing (on 3G and WiFi), performance was pretty poor. Scrolling through categories or through my friends list was sluggish, and some of my friends' avatars have been updated on Xbox Live but are not showing on iNXES. I was, however, able to see profile data, achievements, and game history.