I'm going to my first WWDC this week, so why not give my predictions, along with everyone else? I'll do it in a quick tabular format:

Mac Pro (Power Mac replacement)95%
Garbage collection in Objective-C95%
Low Level Virtual Machine (LLVM)90%
Better integration between Core Data, Sync Services, and Spotlight75%
New Finder75%
Some 3D graphics technology along the lines of Quartz 2D Extreme or Quartz Composer75%
Mac Mini revision65%
New MacBook Pro revision60%
New kernel in Leopard (to replace Mach)5%

Well, let's see how I do. If your going to WWDC, too, stop on by and say "Hello"!