Well, there are enough other interesting things Apple could still release via a special event:
Netbooks for one. Just to get some extra press.
Or the fabled iPod touch based tablet.
I can see that they won't release this in June together with the iPhone to not steal its thunder.
Snow Leopard.
It might come out by the end of this quarter. Or at least get an official presentation and release date somewhen in April.
iTunes event.
Movie rentals, App Store expanded to eBooks and Mac applications, plus introduction of a new Apple TV or perhaps even a real TV set by Apple.
There are possibilities...