I would recommend having a look at the GOG catalogue of games as they have some awesome classics. Good thing about their games also is the fact that they are DRM free and with them being older titles you will have no issues running them.
My favorites out of their catalogue (There is actually more but to many to list!!! ) :
Sacrifice
Giants Citizen Kabuto
System Shock 2
Thief Trilogy
AD&D Games - Neverwinter Nights, Baldurs Gate, Icewind Dale & Planescape Torment
Redneck Rampage
Freespace 1 & 2
Enclave
Legacy of Kain series
Clive Barkers Undying
Dungeon Keeper 2
http://www.gog.com/
Also check out Mastertronics Sold Out Range, they do 3 for 2 on their £5 and £10 (PC Gamer Range) titles with free delivery
I would definitely pick up :
Project Eden
Hidden and Dangerous 2 - You can download the first game free legally, this was done by devs, just Google it
Mafia - One of my all time personal favorites
Medal of Honor Allied Assault
Overlord
Prey
Rogue Trooper & Judge Dredd - Love 2000AD and these are both decent games if you like their respective comics
Stranglehold
http://www.mastertronic.com/
Just take a look through their available titles and see what takes your fancy. Stuff I have listed above are my favorites but everyone has a different taste in their games.
If you aren't sure if your system can run something you can do a live check at the System Requirements website. It gathers info on your system and tells you if you can run a game or not :
http://cyri.systemrequirementslab.com/cyri/
Just type the name of the game in at the top and you will get relevant games in a dropdown under it and just click the one you want. Its really handy tool to use
