On the 15 inch, the following. Same basic case design, but using liquidmetal at least on the keyboard top plate and hopefully on the bottom and top as well.
Two Thunderbolt and three USB 3.0 ports. It's a forward looking move, Firewire and Ethernet compatibility can be achieved these days through adapters, and the more slimline Thunderbolt and USB ports remove an extreme weak spot on the left side of the case around the Ethernet and Firewire ports. Eventually, we should see fiber-optic Thunderbolt replace Ethernet altogether.
Switch from paste to Indigo thermal pads to improve cooling performance without complicating assembly
Gigabit speeds on wireless, maybe with the assistance of a better Airport Express?
Intel's Ivy Bridge processor will likely mean a significant reduction in power, heat and battery consumption, as well as a slight speed boost. Ditto with next generation graphics chip.
Enable customers to get two hard drives or SSDs rather than one hard drive and one optical drive
If Lion has decent user-interface scalability, make 1680x1024 the standard resolution in the 15 with 1920x1200 as an option. If not, and Apple instead goes the IOS route of doubling the display resolution, offer a "doubled resolution" Retina-style display of 2880x1800 or so as an option.
Bring back the virtual numeric keypad on laptops.
Make 8GB RAM the standard, 16GB optional.