You know that annual study that quantifies how much money is lost through hours of unproductive worktime during March Madness? Well, I've got news for the bosses of the world: browser-based gaming is the final frontier of workplace time-wasting. It's not enough that we've got browser-based SNES emulators; these games are getting better and more common. Net Magazine has a great roundup of the top 10 HTML5 games of 2012. The list includes a fantastic Zelda-style MMO, a handsome and handdrawn adventure game, and Dune 2. Yep, the first modern real time strategy game.
If you're worried about getting caught, open so many tabs in your browser that they are impossible to read. Everyone will assume you are so productive you need to have all those tabs open. Suckers. It's the 21st-century version of hiding a comic book inside of your physics textbook.