The first one, the rumored iPhone 5S, is expected to become the seventh iteration in the iPhone series, a premium device that will come with the new iOS 7, the Apple A7 system chip and a brand new fingerprint sensor baked right in the home button. The iPhone 5S is expected to look just like the current iPhone 5 and the only new thing in its looks could be a rumored champagne-gold color version.
The second device that should see the light of day in mere hours is the iPhone 5C, a plastic and more affordable device, that should share many of the features of the iPhone that we know - virtually the same size and screen.
UDPATE: Unfortunately, it looks like Apple is really going to break its habit and won't be livestreaming the announcement. The company will post the video from the event at the following link, but this will probably happen a few hours after the live presentation. You can follow our liveblog of the Apple event to stay informed!