I'm a huge advocate of Google Now and use it on the daily, but the great Google Now style voice search has just reached the latest Chrome stable build for the desktop - version 27.0.1453.93 to be exact.
It's not perfect yet, but it is working as a basic voice search and response service right now. If you want to try it out, make sure that your Chrome build is the latest updated version, if not - click the Help button. From there, give it a few seconds to check your version, and let it restart. When you're back in Chrome, check out http://www.Google.com and then click the microphone you'll see in the search box.
Chrome will ask you for some permission to listen to your voice, and from there you can blast Google for answers.