-Anakin and Obi-Wan duel: it simply couldn't happen any other way, and a volcanic environment is a must. This has been floating around in Star Wars lore since ANH came out, and is quite possibly THE most anticipated event of the prequels. I'd prefer a blue vs. blue lightsaber fight, just to mix things up. Thankfully we're getting all of this!!!
-Episode 3 be titled Revenge of the Sith. Revenge of the Jedi>Return of the Jedi>Revenge of the Sith. Perfect. FAR superior to The Creeping Fear and Rise of the Empire. We got this too!
-Qui-Gon reappear in some capacity. Jinn's my favorite Jedi, and Neeson rules. If the disappearing trick is finally going to be explained, Lucas has said Qui-Gon plays a crucial role, so one would expect him to come back as a voice (again) or even a ghost. With Anakin's downfall, his perspective on things would be very interesting. I haven't heard anything on this yet, but I'm really holding out for this one.
-"Do not underestimate the powers of the Emperor..." Always wanted a Yoda/Palpatine confrontation of some kind, and we're certainly getting it!
-Tarkin plays a part in the rise of the Empire, with his authority over Vader touched upon as well. This character MUST have some sort of introduction, as he's in charge of the Death Star AND Vader in ANH. I've heard Tarkin's at least IN the movie; here's to hoping he's set-up well for ANH.