http://www.paperlesspost.com/session/new
Invitations are delivered in personalized envelopes to guest's inboxes, where a simple click causes them to open.
Past invites, sent and received, can even be archived in a virtual scrapbook.
Pricing begins at $5 for "stamps" to send 60 invitations, and Paperless Post charges a commission on all ticketed events: 2.5 percent on tickets to for-profit events, or 2 percent on those for charity.