At some hobby stores, you can pick up an acrylic molding kit for ~$30 or so. You can mold the Apple in there and pour a new one with the logo inside, or cut a circle into the back of the display housing and then mold a circular with the logo in there as well.

It's a lot easier than cutting, though a saw and file will do as well. You can pick up a piece of acrylic, maybe even already in the size you want, and just cut it out. After it's in shape, you may need to sand the edges and buff them so they don't have an unfinished look.

Oh, the options!
MacBook 2GHz Intel Core 2 Duo w/ 2GB DDR2 RAM & 120GB SATA 5400RPM HDD
Canon Rebel XTI
Google Cr-48 Beta Laptop