A very good alternative to the 580EXII (so I have heard) is
this it can be picked up for around £200 I have read a lot of favourable reviews on it and am looking to get one as a second flash.
I would be very careful with cheap copies on Ebay as I have never heard good reports to be honest I would look for a flash that integrates with your camera i.e. support ETTL and ETTL2 , has manual overides, a good powerful guide number and a swivel and bounce head.