Whether you're a long-time PC gamer or new to the club, (in which case, welcome!) you should check out JogoBox, a game client/downloader similar to the likes of Steam and Desura. What makes JogoBox stands out is that its entire collection is totally free. "Choose from a selection of thousands of free games and play for as long as you like!" -- boasts JogoBox.com.
The JogoBox team essentially went out into the Internet and collected as many abandonware and browser games as they could find and stuck it all in once place -- a simple yet brilliant idea! We were able to play some old classics of the DOS days and rediscovered games that have been long forgotten. Play through oldies like Sid Meier's Civilization, Desert Strike, Command & Conquer: Red Alert, Prince of Persia, and even the original Warcraft! It was worth the install just to play some childhood favorites like Jazz Jackrabbit 2-- a crazy platformer in the same vein as Sonic the Hedgehog and Earthworm Jim-- and Battle Chess, a game that turns the boring chess board into a gruesome battlefield of swords and magic.
Getting it all to work is simple: install the client, pick your game, and hit play. That's it! No credit card to enter, no account to sign up for, and you don't even have to give them your e-mail. The hassle-free process is incredibly refreshing. The drawback is that you are basically a tester. The JogoBox client is currently in beta which means that there will be hiccups (slow response, hang-ups when searching) and it may ask for feedback occasionally, but once the games were installed and launched we didn't encounter any problem. Another downside is that there is not an enormous amount of games despite the claim of carrying "thousands," as the collection only contains a handful of gems. The good news is JogoBox is constantly updating its database and requests can be made through Twitter or Facebook. Check it out here.