Alas, the days of being surprised by iPhone announcements are long behind us, at least from the hardware standpoint. We're now looking at fully working iPhones before they're announced.
Luckily, the iWatch will be a surprise because it's going to be announced so far ahead of it's actual release—probably for that exact reason. There are thousands of "concepts" and "renders" on the web, but no actual leaks.
And, of course, we should get some nice little extras on the iOS 8 side. Even if they're not total surprises, the mobile payment system, Health and HomeKit should all get more in-depth looks on Tuesday.