Allowance in bitcoin
that's pretty cool! The only thing he can buy without asking you is drugs though. (j/k)
I usually paired them with "real" gifts, but gave plenty of Casascius coins as presents this past Christmas. I also gave my niece and nephews "savings accounts" via individual wallets burned to CD, and address payment cards for easy depositing. My niece in particular was thrilled with it; I'll show her how to spend the funds when she turns 18 (although it'll be pretty cool if she figures it out on her own sooner.)
Careful with that, even CDs get destroyed if you keep them in the sun, or if they get scratched. Should be fine if you have a secure backup I guess.
Fake edit: Or in the microwave.