According to numerous sources Google will be introducing a new version of the Chromecast on September 29th during its event in San Francisco. This new version should replace the current Chromecast and offer a bunch of new features including one called 'Fast Play' which will make connecting to other devices quicker and simpler. Other additions expected include some new, faster hardware under the hood, improved Wi-Fi and more. The new Chromecast will also look different and be available in several colors. While retaining a dongle shape it appears more circular in nature in the blurry photos leaked.
Also expected to be announced is an all new product called 'Chromecast Audio' which should offer wireless audio for speakers. We're thinking this might be some kind of bluetooth or Wifi device that does for audio what Chromecast does for video. It should offer both wired ability as well as wireless multi-room audio support.