I love my Converse Chucks, so it only seems natural that my favorite Macbook case would be the Speck Canvas Sport, with its Converse-inspired design. It ordinarily sells for $39.95, but until December 21st, Speck has it for 40% off with coupon code HOLIDAY40.
Sucks for me since I paid full price, but it works out for you. They have other products on sale, though unfortunately not the Specktone Retro (below), an iPod speaker system that I have and love. (Even so, at $99 it's a good deal.)
Now if only Speck would make a Canvas Sport for the 17" Macbook Pro.