I have read that it is bad to put labels on DVDs. The reasoning was that the label, if off centered, could cause a shift in the balance of the disk creating noise. I have also read debates over the issue of whether the adhesive used with the labels was good for longevity, suggesting that it could cause a faster deterioration of the media.
That all said, Memorex use to have a nice kit out that not only came with a devise for applying the labels but also a templet for most all major designing applications, including some non professional but common applications. You would then print the templets with a normal ink jet, they sold special sticky paper that went with the templets.