I'm using a Macbook Air because of the nice hardware and run Ubuntu Linux on it since OSX isn't really usable for me.
Being a Linux guy, I wanted to get rid of the glowing apple on the front for quite some time now. There was of course a catch: The apple should be replaced with something nice that integrates the glow in a cool way.
The first stickers I found were on Etsy, search word here is macbook decal. Unfortunately, most of the badges keep the apple logo and only some integrate it at least partly, but nothing was nice enough for me.
After a while I found macstix.net which exclusively have labels that cover the apple and let other symbols glow instead - see their gallery. I contacted them, sending a SVG file along how I imagined the sticker could be. Unfortunately they had to decline but told me the address of their competitor: iDiffer.
The iDiffer guys answered quickly, measured, tested and finally made the sticker for me. It costed 19€ in total, and today it arrived:
Update 2013-08: Separate sticker page
iDiffer has a separate page for the tux sticker now, and it costs 8€.