It’s about time somebody did this. From Lifehacker:
Tired of being left out of private betas? Not to worry – try InviteShare, a service that encourages those with beta invites to share them with the Web community at large. Here’s how it works: people with beta invites share them with those who don’t have them – it’s super simple. Plus, while e-mail addresses are displayed publicly, they’re in image form, which means no spam bot attacks. This is a great way to get in on services before they’re open to everyone.