Open Space is an innovative and rather daring way to run a conference (originated by Harrison Owen). The basic idea behind it is that the control of running an event should be given back to the people who matter the most -- the participants! (In this, the concept is quite in line with Agile that similarly strives for empowerment of the team.)
My experience with Open Space has been Barcamp in India. It is a fun way of doing things which leads to productive results ("fun" does not have to mean "non-serious" after all). It enthuses everyone -- the participants, the speakers and the organizers -- with great energy and a heady feeling of being part of something important.
You can find out more about Open Space by reading Martin Fowler's bliki entry.
So next time you want to organize an event, you might wanna give this a shot!