While we're throwing out links, here's a link that I check regularly for good PC deals:
http://www.steamgamesales.com/stores.php
Despite the fact the link says "steamgamesales", it also covers current sales from Gamers' Gate, Impulse, Origin, and Direct2Drive.
In my opinion, Gamers' Gate is the best of the services since it adds absolutely no DRM. However, Steam does offer social networking, automatic patching, achievements for specific games, and occasionally cloud saving.
There's also OnLive for playing PC games via streaming. I haven't tried it myself but it would obviate the need for a robust gaming PC.
http://www.onlive.com/