At OfficeMax I've seen labels specifically for CDs, and they sell a kit, with templates and such, so you can do the artwork and churn them out on your printer, and also, I think, a little doohickey to help you actually place the label in the middle. With a scanner you could probably adapt the original artwork and make a sleeve and a CD label for a fine end-product.

(Then of course, a label costs about as much as a blank CD, and printing full color on an inkjet printer will use up your ink pretty fast.)

I admit I haven't tried any of this yet myself, but I'm thinking of adding one of those combo scanner/printer/copier jobbies to my office equipment.

Or you can use a Sharpie fine-point permanent marker.