A girl I know asked me this question the other day, and it truly perplexed me. I suppose that the knee-jerk reaction is something along the lines of my car, or my apartment. But really, I think that it's a little deeper than that.
I would have to say that my most prized possession is my CD collection. I have about 500 CD's (not burned CD's), and I've been accumulating them for over 10 years. I have a lot of imports and rarities, and I feel like I have a very comprehensive collection that is fairly representative of many genres of music and is very high quality, i.e. I have never been suckered into buying "one-hit wonders."
Anyway, I'm curious to see what y'all think!