iPhone 5
The new iPhone WILL be called the iPhone 5, it doesn't matter if it looks the same (or slightly different) on the outside to the 4, it is going to be the 5th generation model so it will be called iPhone 5.
I think the reason you have not seen any leaked parts or images of new designs is because there aren't any! If there were, they would have been leaked by now, just like the N94 parts we have seen. Right now there must be at least a million iPhone 5's in storage in China and by now someone would have sneaked one out and shown it off especially if it was a different shape. But my guess is they looked at it and thought - it looks the same as the old one, so who would want to see it?
I don't believe that Apple will release two phones either - they never have before and they have no need to do it now. Hell, they could keep selling the 3GS if they wanted, it will run iOS 5 after all.
The trouble is, people on this (and other) forums think that everyone else in the general population is waiting on the edge of their seats for this new phone too, but they just aren't and Apple knows this. Apple knows that there are a lot of people still using 3G and 3GS iPhones. These people are at the end of their 2 year contracts and are ready to upgrade to a new iPhone.
I can't see why some of you think that if they don't change the outer shell they would be in trouble. Remember, they kept the same design for the 3G and the 3GS and nobody complained - they sold loads of them. Most people, will buy a case anyway, so why should you care what it looks like at all. In fact, if it does not have a teardrop shape, then perhaps some enterprising case maker might design a case that is that shape and sell it to all the people who wanted it to be!
Also, to the whiners who say "well that's it, if the phone does not look different on the outside, then I'm going to buy XYZ Android phone" (I think there's about 3 of those so far on here), I say go on then, put your (or more likely, your parents) money where your mouth is and buy your Android phone - it will suck and every day you'll wish you'd bought the iPhone for the duration of your contract.
Anyway, not long to wait now - I just want iOS 5, Lion, iCloud and iTunes to be released on the 4th (or 5th if they want to do the whole 5's thing). I'm not going to be buying the new iPhone whatever it looks like, but I'll still be getting a new iPhone without spending a penny!