Sure, Amazon's Cloud Player works -- as long as you're in the U.S. or willing to do some tinkering -- but it's fairly simplistic at the moment. There are plenty of features missing which we'd like to see added -- but since Cloud Player is a Web app we don't have to wait for Amazon!

Google Chrome users, for example, can add playback hotkeys with an extension called keyMazony. Once installed, you'll have keyboard control of your Amazon Cloud Player queue. keyMazony commands will work as long as you're in the same Chrome window as Cloud Player, even if its tab doesn't have focus. The key combinations are customizable as well -- just make sure you don't set up a combo that conflicts with another extension or Chrome's built-in keyboard shortcuts.