I'd recommend Rollercoaster Tycoon 2/3, pretty fun games and you can be quite creative, too. I wouldn't recommend a driving sim but I do like Gt Legends every now n then. Something like FSX can be pretty relaxing for a flight sim. Once you get used to it and/or stick to just a casual fly around a few scenic areas. There's a nice little mission where you have to fly a little cesna over a mountain top after running out of fuel and making it to the nearest airport. It's good fun, it does get a little boring but, every now and then when you feel like taking a private jet out for a fly around it can be a good way to pass the time in a fairly relaxing manner. It might be a little taxing on a system that isn't as high end as it could be, though.
Pro Evolution Soccer is another stressless bit of enjoyment for me. It depends, though, once you get the hang of it it's great fun on the hardest skill setting, two player mode is the best or playing online but, that sometimes can be stressful getting beaten by some kid who never stops playing it.
Not sure what else I'd recommend, those three or four games are all I find myself playing. Fallout3, FarCry2, Crysis etc etc, they all just bore me after a few minutes. The same old shooting countless bullets into this or that and not really doing anything too clever.
The original Max Payne was great fun for me. Again, once it becomes second nature using your bullet time and aiming for certain areas on your enemy......It's a good bit of entertainment, more so than FEAR.
There are also games like The Lost Crown -A Ghost Hunting Story which I've had a little go on. It's fairly enjoyable as you go on your quest to find out what the hell you are doing in this weird ghost town and start looking for evidence of paranormal activity, I didn't give it all that much time but every now n then I think I would like to have gone back to it and complete it. It had some nice atmospheres at times, if a little tedious, maybe.
After that, there are games like World of Goo which I've heard to be quite good fun, a sort of lemmings game but with goo...You'll have to do your own research on that, don't know much about it. Snooker games are also quite nice to play. I'm hoping there will be a new version of World Championship Snooker coming soon, haven't really been listening out for news on it. A friend of mine loves playing that.
An overly wordy reply but, maybe it'll help..