Maybe biased because I've had an '06 and now ride an '08, but the Enduro seems to be the one bike that has just kept on being a classic from it's inception through to now.
People will say the '03/04 was the best (I haven't ridden one, so wouldn't know) and others will say the '05/06 is the best (it was an awesome bike). The naysayers will argue that the '07/08/09 version has lost some of the qualities of the old Enduro, but swing a leg over one and wow – it's amazing. Just read the Specialized forum on MTBR for some views.
The 2010 version is a bit of an ugly beast imo, but I'm sure it will ride amazingly well. Has any other bike been so consistently good for so long?