Thought you might be interested in this. Just read this post on Strobist about a new, very cheap, powerful flash that may interest you. You could get several of these for the price of one 580EXII!
http://strobist.blogspot.com/2010/08...uo-yn-560.html
There's also the Lumopro 160:
http://strobist.blogspot.com/2010/06...-sync-v20.html
(I have a couple of the predecessor Lumopro 120)
And of course the Nissin Di866 I've previously reviewed here.