The Internet Archive has put together a collection of classic arcade games that you can play for free - all in your browser. These games range from awesome "Q-Bert" to "Frogger", "Golden Axe" and even "Kung-Fu Master". If you want to get your classic game on, take a look at the link below. Also, make sure to check out their Historical Software Collection, that includes classic games as well as classic OS'.
The game collection ranges from early "bronze-age" videogames, with black and white screens and simple sounds, through to large-scale games containing digitized voices, images and music. Most games are playable in some form, although some are useful more for verification of behavior or programming due to the intensity and requirements of their systems.
Source: InternetArcade (Archive.org)