From what I gather, the iPad is using iPhone OS, but with a different screen resolution from the iPhone and iPod touch. So many sites may have to change their user agent detection to adapt to the iPad.
So, can anyone with access to the iPad or the iPad SDK give us the user-agent string?
iPad 2 under 4.3.5:
From Simulator 3.2 final:
I think it is worth mentioning that you don't generally need to use the whole agent string, unless perhaps you find a reason where you need to tailor the website to a specific model.
You can check for iPhone, iPad and iPod in the agent string and cover all your bases.
Here you go!
Safari on iPad user agent string in iPhone OS 3.2 SDK beta 3:
More info: http://developer.apple.com/library/safari/#technotes/tn2010/tn2262/_index.html