Oh jeeze, so many!
My first ever PC games were in a collection box of Theme Park World, System Shock 2 and something else that I can't remember, I then moved onto Theme Hospital, The Sims, then the next jump was when my brother in law bought a new PC and he played Aliens vs. Predator 2, Max Payne etc, but then you can move up another era to CoD, Far Cry, there are just so many at different stages! Vietcong haha that was awesome too, and watching him play The Thing, and Mafia! Ohhhh!
Edit: If you can include consoles my brother in law had an N64 so I used to love Goldeneye, Perfect Dark (the multiplayer side) road rash or was it road race? Smacking people on bikes with a bannana lol. WWF Wrestlemania 2000, WWF No Mercy. I had a PS1, Medieval, Tarzan, WWF Smackdown, I can't even be bothered naming them all lol.