Give-a-Song.com, a group of international singer-songwriters, offers custom-created songs for unique gifts.
The idea is simple. Pick a singer-songwriter out of the several different musical genres offered, choose a song, and then send them your personalized details. They'll then re-record the vocals, and you'll have a unique song sent on CD or via MP3.
If you want even more personalization, they also offer a full original song service, where they'll write and record a completely new song to your requirements.
Turnaround times are from a quite insanely quick 24 hours worldwide (for MP3), and prices begin at only £39.99 ($79.99) too, so it's certainly not something that only the super-rich can afford.