"Must Own" sims for sim fans

I just got IL2 in the mail and am very impressed. There are lots of "classic" sim games out there and I think any simulation fan should own all of them. The prices on most are very reasonable now and anyone who hasn't occupied some of their hard drive space with the classics is really missing out.
So, as a public service I'd like to start a list of my favorite modern classics (stuff that'll run on a modern windows machine without too much difficulty). I don't want this to be a debate of "that one's good, but XXX is better". Let's face it: they're all good. So please add to the list as you see fit. I'm sure other's recommendations will have me loading at least one or two more sims on my hard drive (don't worry, I have plenty of room.) :)
Microsoft Flight Simulator (all revs)
Falcon 4.0
Lock On Modern Air Combat
IL2
Richard Burns Rally
Grand Prix Legends
all of the Simbin titles (GTR 1&2, Grand Touring Legends)
So, as a public service I'd like to start a list of my favorite modern classics (stuff that'll run on a modern windows machine without too much difficulty). I don't want this to be a debate of "that one's good, but XXX is better". Let's face it: they're all good. So please add to the list as you see fit. I'm sure other's recommendations will have me loading at least one or two more sims on my hard drive (don't worry, I have plenty of room.) :)
Microsoft Flight Simulator (all revs)
Falcon 4.0
Lock On Modern Air Combat
IL2
Richard Burns Rally
Grand Prix Legends
all of the Simbin titles (GTR 1&2, Grand Touring Legends)