Even though I only know a few celebrities actual xbox live gamertags, I decided to make a post dedicated to them. This will be a running list, so if anyone knows any other celebs or famous people’s gamertags, post them in the comments. Out of the whole list I’ve only played Modern Warfare 2 with Robert Kelly and he seems like a good dude. He actually invites me to his XBL parties all the time whenever he sees me playing MW2 and he uses his headset to chat it up. So while he may not be as popular as some other comedians/stars it’s nice that he actually participates in the games.
Confirmed
Lord 187x – Ice-T (Rapper/Actor)
SouljaBoyTellEm – Soulja Boy Tell Em (Rapper)
MRxzibit38 – Xzibit (Rapper/Actor)
YouStink2 – Robert Kelly (Comedian)
DURST LBGC – Fred Durst (Limp Bizkit Singer)
Estaban85 – Chad Ochocinco (Football Player)
tonyinegypt – Tony Hawk (Skateboarder) – May or may not be temporary (based on the “in egypt” part), but he posted it on Twitter
Those few above are confirmed via videos, twitter, etc. The list below are UNCONFIRMED, found on random forums and other sites. The ones that end in GWF are “Game With Fame” Gamertags and probably no longer work.
Unconfirmed
50 Cent – Kid4Life
Bill Gates- MSgates123
Colt Cannon (famous skateboarder)- Coltron3030
Adrian Peterson- SoonerPride28
Matt Leinart- KingofTroy11
Jenny McCarthy – JennyGWF
Dave Navarro & his band- PanicChannel
Method Man – MethodManGWF
Members of the band O.A.R. – OARMarc, OARBenj,OARJerry, OARChris, and RichOARd
Ryan Pratt (from ListAfterList) – EarsP
Michelle Rodriguez- MRodriguez
Willis McGahee – WMcGahee21
Dan Cody- OKDanCody80
Grant, the bassist from underoath: youmissedme
J Allard (Xbox team) – HiroProtagonist
Mei Mei Bong (xbox team) – DragonLady
Dane Cook – DaneCook
Senior Editor of the popular gaming review and info site, GameSpot – GameSpotting
Gilbert Arenas – AgentArenas
Andy Roddick – AndyGWF
Jim Carrey – Jim_Carrey
Mr. T – T100
Chingy – ChingyGWF
Michael Halford – Coola
Bill Gates – MicroBoy
Ludacris – xrider
Bam Margera – Gumball 3000
Brady Quinn – BQuinnGWF
Paul Wall, the rapper – T Paul Wall
Shia LaBeouf – ShiaGWF
Eminem – your_an_idiot2414
Dave Mustaine from Megadeth – DMustaine
Jason Giambi -giambiGWF
Charlie Frye (QB of Cleveland Browns) – BT67

Played cod MW2 with Zac Efron a few times. I met him on xbox through a friend of a friend who’s friends with him. His gamertag is Beach Stud. I wouldn’t bother sending him a friend request though, he only adds people he knows.
Jhonen Vasquez was on Game With Fame, that gamertag was Bioshock2Jhonen . but like you said it probably no longer works.
I was informed that Christian Finnegan, the comedian, has an Xbox Live gamertag that is something like ‘MC Mustache’.
DURST LBGC is no Longer Fred Durst’s xbox live gamertag. it has recently been changed.
so it is confirmed to be wrong.
actually matt’s leinharts gamertag is Xxsucks at footballXx