Vyte

Vyte is the iPhone calendar app that actually helps you schedule meetings faster. You can suggest several times and places when you create an event and your invitees get to vote on them without having to sign up or download the app. Confirm the best date and place and everyone get the final invites in their calendar.

If your invitee has already signed up for Vyte, then you get to see her availability overlaid in your calendar as you suggest dates!