robinhood.io has done a pretty kickass job of building hype. You enter your email address and get added to the back of a queue. But if you share (and get other people to sign up) you leap-frog over the others in front of you.

Here's another one. When MeteorJs announced "Meteor Developer Accounts" they sent out an email blast saying "Claim your Meteor developer username". And people (like me) scrambled to reserve the username they wanted before it got taken. I thought that would be a pretty damn awesome way to prelaunch anything that has user profiles / usernames. (Reserve your username in advance of our product launch)