Don't know what games you have lying around, but I'm playing through Command and Conquer: Red Alert 2 again right now and boning up for the expanion pack that I'm picking up tomorrow. That's a really fun RTS if you haven't tried it already. I was also playing through No One Lives Forever again recently, which is probably the best single player game to come along since Half-Life. Of course there's Max Payne, which is the best single player game to come around since No One Lives Forever.

If you've been out of the gaming scene, I'd say those three are probably the best ones to pick up. I'm assuming you've already checked out Diablo II and its expansion pack, which are probably the most popular, although that's not what you said you liked most. I've also heard good things about Red Faction, but I checked out the demo and the graphics were pretty weak, and most of the reviews said that it's really short, but fun.