Not done yet with your seasonal gift-grabbing and got a few extra grand burning a hole in your pocket? Yeah, us, either. But if you're, say, Robert F.X. Sillerman, you might want to hightail it to Christie's. Today, the auction house will sell off more than 400 pieces of rock history — including a Gibson guitar once owned by Beatle George Harrison, Madonna's "Like a Virgin" veil and a grade-school book report by Britney Spears. (See? She can too write. Not well, but still...)