Steam Sales and Humble Bundles, if you're into PC gaming. If you're not... all I can suggest is wait a very long time (but not too long or else they go back up in price for being retro). :( It can be hard to get crazy good deals on console games.
Seriously, though, Steam is so great for getting deals on games. I hold every other kind of video game sale to its standard nowadays. I have thousands of dollars worth of games on my account but can't have spent more than a few hundred dollars on everything. Even if your computer isn't great, there are plenty of indie games it should be able to run and older games go for extra cheap too, especially during sales. (GreenManGaming almost always has a 20% off coupon too and most games activate on Steam.)
Gaming PCs cost more than buying a console, but in the long run they are just so much cheaper because PC gaming is so much more cost-effective than console gaming. @_@