Apple has released the third beta of iOS 5.1 to developers. iOS 5.1 beta 2 was released nearly a month ago, but now that the holiday lull is out of the way it's probably not going to take that long before the next beta comes out.
The beta is available both through over-the-air download and a direct download link on the Apple Developer Center website.
Once released, iOS 5.1 is expected to introduce improvements to Photo Stream and address battery life issues that some users, particularly iPhone 4S owners, have experienced in iOS 5.
Apple iPad Air 2
Apple iPhone 6s