Amazon Web Service 4.0 (Beta)
Just got the invite from Amazon to take part in the Beta for the 4.0 WS Release. There's a lot of cool stuff in it - if you're interested, I'd encourage you participate. So far I've used Google's Web Service (API) and Amazon's and while they are still pretty young, they aren't short on functionality. Besides, using a commercial web service confirms that your app is connecting correctly and all that jazz and all in all, it's just plain cool.