Apple has rolled out iOS 5.1 beta 2 to developers which includes some bug fixes, and also allows users to remove images from their iCloud Photo Stream.
iOS 5.1 beta 2 weights 801 MB and its compatible with iPhone 4S, iPhone 4, iPhone 3GS, iPod touch 4G, iPod touch 3G, iPad 2 and iPad.
You can download iOS 5.1 beta 2 via iOS Developer Center.