Hardware (Most to least likely)
Macbook mini - ultra mobile laptop, without optical drive, nand flash based storage, led backlit etc. i'm going to say either a 12 or 13" screen is possible. some sort of additional "wow" feature, wether this includes some gestural recognition or not, i think there is something else than just a lightweight laptop behind the curtain. I'm going to idealistically say this is the iMac styled docking station mentioned on AI just recently.
Macbook Pro - new models, new enclosure, faster processors, better graphics cards... it would make sense for Apple to include Blu-ray in a mobile form simultaneous to a Mac Pro update.
Mac Pro update - Blu-ray and perhaps new graphics cards... not a system overhaul but more current hardware offerings for such an expensive tower
Apple Cinema Display - probably newer LCD panels, higher quality. I doubt to see a huge refresh using any new display technology... just need to keep them comparable with what other manufacturers are offering. Hate to say it but Apple displays have never been very impressive.
iPhone - 16GB capacity, perhaps better camera capable of video recording.
AppleTV - needs 1080i out at least, perhaps ties in with an announcement for HD rentals from the iTunes store
Mac mini - dead or updated... really tough call, but if they kill it off, I'm going to buy one immediately.
Software (Most to least likely)
iPhone SDK - I think there will be alot of talk about this, and introducing what some higher level third party developers have already been working on
Leopard - Carrying on about how awesome it is, and how great it works with .Mac and iLife
...hard to see what else could be talked about in regards to software, pretty much all of Apple's software is new and fresh, I think an Aperture update would be appreciated by many.... I'm thinking a hardware heavy Keynote address.