- get a CPU with VT (Virtual Technology) capabilities enabled. This will enable you to install virtual machines easy
- get as much RAM as possible. This will help virtualization as well
- get as much HDD as you think will be necessary. I would not go SSD route (unless you get 17" laptop with two HDD bays)
- last, but not least - get matte (non-glossy) HD screen (1920x1080). Everything else is upgradeable later on
At least here in USA, retail stores do not seem to stock laptops with HD screens (they are more expensve, therefore harder to sell), but at least Dell have XPSs with good screens.