Hi there. There is a good one out now called 'ALEXANDER'. I think it is based on a film due out but this one looks incredible.
http://www.alexander-thegame.com Check out the screen shots.
Also look back at some old ones. Boulderdash is easy to kill an hour or two, just google it and you can download it free.
Another oldie but goody is the old Cannon Fodder games, 1 & 2. I have them here if you want me to send them up to you just let us know.
Good games with a bit of action in them would be the cracking Half-life and now you can get Half life 2 but you need a good spec PC to run the new one.
Another new one is 'ROME' You can also play this on line too I think. It recently got a 97% in a gamer mag and that is pretty good. Rome 'Total War' This looks like the favourite at the moment.
Does he know anything about football? Maybe he could have a go at something like a football manager sim, they are quite popular thesedays too.
Just racking my memory and thought of a good one from a few years ago called 'TOTAL ANNIHILATION'. It can take years to complete, the maps are massive with huge battles taking hours to finish, it must be one of the most underated games ever.
Also have a look out for a game called 'ELITE'. an old classic that is/was voted the best PC game ever. That should keep him happy for a few months at least.
If I can think of any more I will post back but do consider the games mentioned above. Try Amazon of ebay for the older ones, worth it in the long run.