This has been on Major Nelsons blog for a while so not exactly sure when this promotion will end but if you use these 360 codes you will receive a free Bing search engine T-Shirt for your 360 avatar. The male avatar shirt comes in black and the female one in White.

Male: PHT9P-KXR4Y-BB6BY-VFMPD-THT4T

Female: VFH6P-9FJKK-KKP9G-H4DRH-WTCFM

In case you don't know how to redeem a code. Hit your middle home button then scroll to the far left till you see the option "Redeem Code" from there just type in which ever shirt code you want. You do not need to put the dash since it will do it automatically.