1. iPod touch, radically new design like iPhone 4.. retina display, A4 SoC, Front face camera, etc.
2. iPod nano, possibly a touch screen interface with an even smaller form fact as the screen takes up much of the surface.
3. Cloud based iTunes store accessed via a web browser.. something Apple has been working on for some time, part of it is already accessible and used publicly with iTunes links.
4. iTunes 10, possibly rebuilt with Cocoa.
5. iOS 4.1 released for iPod touch, iPhone 4, and iPad... adding in support of Apple Accounts to be used with FaceTime so that iPod touch users can use the feature (right now FaceTime requires a cell phone number). Other features include things such as printer support, which has been slated for a later release as said within the readme file of Pages on the iPad.
6. Possibly iMovie for iPad.
7. Possibly, but highly unlikely, a new rebranded AppleTV (iTV) for $99 running a hybrid of iOS. I see this coming around October, but it may pop up at this event.
8. TV Rentals.
The Live Streaming thing is something Apple has been working on since 1998. They tried with the open source Quicktme Streaming Server, and had a feature in QT called QT TV, you could watch broadcast stations and streaming media from the Quicktime player. This eventually failed. Around 2008, Apple began steadily working on a new open standard using the HTTP protocol. Since then, they have added it to iOS, Mac OS X, and AppleTV. I do believe this will turn into something big down the road, I'm not quite sure this event will have it.. or if Apple will wait till a later date such as in October. the live stream will be using HTTP streaming, which is why it requires iOS 3 or higher, or Mac OS X 10.6... as it hasn't been implemented in a large scope yet.