From Microsoft's own site:
http://www.windowsphone.com/en-US/features-8-1

For additional reading from some of the fan boy blogs, that typically have good/accurate information (note there are 5 pages):
http://www.wpcentral.com/windows-phone-81-review

I'd start there anyways. One piece of advice, if you do go the Windows Phone route over Android, get a Nokia, and probably something like the 920, 930, 1020 or if you really want a big screen 1520. The Icon on Verizon I hear has great reviews, and the 925 is solid on T-Mobile & AT&T. Nokia (now Microsoft), has a very strong track record of updating their phones, something that can't be said for Samsung and HTC. I've received at least 4 updates on my Lumia 1520 so far. Nokia also does a lot with extending the capabilities of the phone. Things such as the glance screen and the call blocking capabilities.