What is the iOS 5.0 user agent string?
iPhone:
Mozilla/5.0 (iPhone; CPU iPhone OS 5_0 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A334 Safari/7534.48.3iPad:
Mozilla/5.0 (iPad; CPU OS 5_0 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A334 Safari/7534.48.3
This site seems to keep a complete list that's still maintained
iPhone, iPod Touch, and iPad from iOS 2.0 - 5.1.1 (to date).
You do need to assemble the full user-agent string out of the information listed in the page's columns.
I found a more complete listing at user agent string. BTW, this site has more than just iOS user agent strings. Also, the home page will "break down" the user agent string of your current browser for you.