quad core
faster everything
more hd space
a redesign
a crap load of options on specs
There are no quad-core chips yet, and the Clarkdale chips won't be at high enough clock speeds for Apple to likely put them in. Arrandale is far more likely, and runs only on dual-core levels (albeit with 4 virtual cores).
A redesign is not likely, especially since Apple matched the laptops recently to match the iMac.
More HD space is likely coming, now that WD has 2 gig drives available.
A lot of options, also, not likely.