One of my favorite PC games was RollerCoaster Tycoon. I can't stand actually going on thrill rides, but I get a bizarre amount of enjoyment out of building them. Sadly, it's been a long time since we got a new game in the series. Well, maybe this is the next best thing: an add-on for Half-Life 2's Garry's Mod that lets you build and ride roller coasters in first person.
You can check a video that demonstrates how this all works after the jump, or you could just download it here.