Which iOS devices do not support iOS 5?
Devices not supported by iOS 5:


iPhone (original)
iPhone 3G
iPod Touch first generation
iPod Touch second generation
AppleTV


Source: http://www.apple.com/ios/features.html . "iOS 5 is compatible with: iPhone 3GS, iPhone 4, iPhone 4S, iPod Touch 3rd generation, iPod Touch 4th generation, iPad, iPad 2."