Half Life 2
AvP1/2/2010 (in certain areas, Alien usually)
Stalker SoC
Crysis (Lift sequence and subsequent Alien Ship areas)
Any FPS which involves a lot of fast moving in narrow/confined areas (ie. Crysis ship levels)
All make me motion sick. They give me the worst headache with vertigo and can do so within 10 minutes and I have never found out why. This hit me at 18/19 with HL2 yet I used to play Quake 1/2/3, CS and HL competitively on a LAN when I was 11-16 against adult opponents and never had the glimmer of an issue.
Homeworld
Every time I hear Agnus Dei by Samuel Barber there is an instant sadness and chill going up my spine. Everyone who is anyone remembers Mission 3.
Command & Conquer: Red Alert
Not only was is a great RTS (my fave until probably DoW or CoH, HW was close) but it helped me form a decent Russian accent, or at least I think it's pretty good. Just needs practice
A-Train
This game was phenomenal. Similar to Sim City but focused more on train infrastructure and building of amenities. When asked in class aged maybe 7 what buildings you'd find in a city, I suggested a Lease Building and was told my suggestion was incorrect. I was kinda like 'What? It's in A-Train so it's got to be a real building".