Apple has released iOS 5 beta to developers that is compatible for for iPhone 4, 3GS, iPod Touch 4G, 3G, iPad 2, 1 and Apple TV 2G.
Apple unveiled iOS 5 at WWDC 2011 Keynote, which includes more than 200 features for iPhone,iPad and iPod Touchusers such as Notification Center, iMessage, Newsstand, Reminders and Twitter integration. Apple has also improved the Camera app, Photo app, mobile Safari browser, Mail and Calendar app in iOS 5. With iOS 5, users also won’t need a computer.

You can check iOS 5 features which we have listed before.
Although iOS 5 beta is available for download through iOS Dev Center to developers only but if you still want to try it out then search the following download queries in Google Search.
Download iOS 5 Beta 9a5220p
Note: To use these you must have your UDID registered with a Dev account.
iOS 5 Beta for iPhone 4
ios_5_beta__iphone_4__9a5220p.dmg
iOS 5 Beta for iPhone 4 CDMA
ios_5_beta__iphone_4_cdma__9a5220p.dmg
iOS 5 Beta for iPhone 3GS
ios_5_beta__iphone_3gs__9a5220p.dmg
iOS 5 Beta for iPod Touch 4G
ios_5_beta__ipod_touch_4th_generation__9a5220p.dmg
iOS 5 Beta for iPod Touch 3G
ios_5_beta__ipod_touch_3rd_generation__9a5220p.dmg
iOS 5 Beta for iPad 2 GSM
ios_5_beta__ipad_2_gsm__9a5220p.dmg
iOS 5 Beta for iPad 2 WI-FI
ios_5_beta__ipad_2__9a5220p.dmg
iOS 5 Beta for iPad 2 CDMA
ios_5_beta__ipad_2_cdma__9a5220p.dmg
iOS 5 Beta for iPad 1
ios_5_beta__ipad__9a5220p.dmg
iOS 5 Beta for Apple TV
ios_5_beta__apple_tv_software_beta.dmg