All of the AC games, except AC3. They came out in a bundle on steam during some sale, and it was like 25 euro for the lot so I was totally having that.
LOTR: Battle For Middle Earth, bought it when it was new, and somehow it got stuck at some teacher's office 2 towns away from here with train. This was years later, and when I checked the local store it was actually cheaper to buy a new one, train ticket would have cost more than double. Also the teacher was a right **** so I didn't really want to speak to her ever again.
Vampire The Masquerade: Bloodlines. This is probably my favourite game of all times and I bought it again on Steam for ease. Installing from 4 CDs is such a pain heh.
GTA 3/VC/SA. I honestly have no idea where all those disks went, lend out to various people that I've now forgotten I guess. Again a Steam Bundle got me to buy seconds, literally all PC GTA titles for 6 bucks, can't beat that kind of value.
Too bad GTA 4 is so hideously boring.