Obviously, Illustrator CS4 is a part of that announcement. Want to know what's in Illustrator CS4? I can't tell you -- YET anyway. But you can be sure that on the 23rd, I'll have all the info you'll want... and maybe even some more... (oh I love to tease)...
In any case, be sure to clear that day, because we're going to have LOTS to talk about -- you and I -- oh yes. OH YES!
By the way, you can head over to Adobe.com and register for their online event.
UPDATE: Considering we have some time on our hands, I thought I'd compile a list of known details about future Adobe products, compiled from other sources on the 'net. Note that this list is purely hypothetical, considering that while Adobe has shown these technologies in public (usually at conferences or large public gatherings), they are always shown as "technology previews" and hence aren't guaranteed to appear in a particular version. That being said, if anyone has more items to add to the list, let me know!
ALL APPLICATIONS: Based on public betas we've seen of some CS4 apps, it appears all new CS4 apps will feature a new unified user interface.
ILLUSTRATOR: At the Icon conference in NY this past July, Adobe showed a paintbrush-like tool that paints with expanded paths and that can auto merge with other existing paths.
PHOTOSHOP: Several websites have spoken about OpenGL support for increased pan and zoom performance.
FLASH: Several sneaks at some Flash conferences have previewed 3D functionality as well as something called Inverse Kinematics.
INDESIGN: A sneak peak at several conferences revealed a Flash export capability as well as a format where InDesign content could be brought directly into the Flash application.
DREAMWEAVER, FIREWORKS, SOUNDBOOTH: These CS4 apps have been available as a public beta download at Adobe Labs for some time now.