For those of you who are not so tech weary or into PC gaming at all,
Steam by Valve would be the tool to get you interested. Steam allows for users to download the application free from the "Steam Powered" site. This application allows for:
Finding new games
Watching trailers
Trying demos of hundreds of games
Plenty of discount prices
AAA titles easily accessed
Incredible packages with incredible savings
Increased multiplayer functionality
Support forums
As said by Jesh, Steam is like the Xbox Live of computer gaming. Initially Steam was a small program for Valve developed titles but lately it has grown larger than that and harbors many "Game of the Year" titles such as Call of Duty 4, Half Life 2, Bioshock, Fallout 3, and many other expansive titles.
With an easy to use interface, Steam allows for even the un-tech savvy to enjoy gaming at their desktop. If you are still unsure if this is right for you, plenty of "indie" titles are around for the more casual gamer with hits like Trackmania, Bejeweled, and Audiosurf (personal favorite).
pc technology gaming related steam bioshock call of duty
They have a bit of an advantage because they can probably 'convince' publishers who are doing Xbox / PC games to only sell their Xbox game ports on the Windows service.