In the iconography of the worldwide indie scene the good ol' cassette has almost become what the cross is to the christian church. Cassette shirts, bags, necklets and other stuff is worn even by teens that have most probably never ever used MCs. I am sure you own at least one of these items yourself. Although everyone got kind of fed up with the whole cassette thing I recommend you this following gimmick as the perfect birthday gift.
You can use it as mp3 player (although the maximum is only 2gb) and you can play it with any cassetteplayer like old car stereos.
If you buy it and don't know which songs to put on it, check these out:
Foals - Olympic Airways (Ewan Pearson's Return To The Villa Of Joy Remix) (mp3)
Housse De Racket - Oh Yeah! (Gonzales Remix) (mp3)
Bloc Party - Talons (Acoustic Version) (mp3)
(of course you can put these songs on any other mp3 player, too!)