I never got into the original Sim City, but I did create some very nice (and time consuming) cities in Sim City 2K.
Red Alert 1 is an amazing game, which I owned before I got C&C so I didn't play much C&C even *when* I did get it.
I still play Doom 1, 2 and final doom today... I have the collectors edition with the doom 95 front end that works well on Windows XP.
Duke Nukem 1, 2 and 3D are all very good games with the first two becoming almost addictive. The third has some great one liners and some funny scenes in it...
I never did get into Quake 1 and 2, I guess I just don't enjoy the theme all that much.. However I did play Doom 3 and Unreal Tourny for a bit.