Apple has released the second beta of iOS 5 following it's announcement during the WWDC 2011.
The beta version will only be available to developers who have enrolled in the iPhone Standard or Enterprise Program. If you are enrolled you can access the download links here.
The first beta of iOS 5 was released on the 6th of June. The final version of iOS is expected to be released during the fall of this year alongside a new iPhone (4S/5).