Lion Recovery Mode

You can run Disk Utility to check or repair your hard drive, erase your hard drive and reinstall a fresh copy of Lion, or restore your Mac from a Time Machine backup. You can even use Safari to get help from Apple Support online. And if Lion Recovery encounters problems, it will automatically connect to Apple over the Internet.

This is built-in to the new Mac Minis and MacBook Airs. No hard drive/CD/DVD/flash drive required. Awesome!