I bought my first Episode III tie-in product yesterday when I picked up the new soundtrack. (Ok, I suppose I bought the bag of Dark Side M&Ms, but those don't really count. ) I can't imagine what I'd do with all the figures you guys are collecting.
The soundtrack is pretty cool, although it doesn't sound like there will be a new standout theme for this movie - a lot of the character themes are reprisals from the other Star Wars movies. (Including the original trilogy.) I'll need to wait to hear the soundtrack in context in the film to really judge it.
It does come with a bonus DVD though of a lot of classic Star Wars music played with images and scenes from the movies.