As a pre-order bonus some copies of The Beatles: Rock Band included a code to get a T-shirt for your avatar.
This was in the US only but it’s possible to pick one up from eBay if you’re lucky. Here’s a male T-shirt @ £2.40 (there are 8 available to buy now at the time of writing). I don’t know if the code works only with a US account but from reading this thread on the Rock Band forums it seems they are international. There were a lot of codes traded and handed out and it seems some from outside the US managed to get them. Please let me know if these codes are 100% US only or not.