'06 LeMond Versailles, '04 S&M Beringer, '03 Quamen Bowls, '68 Raleigh Grand Prix (converted to fixed gear)
RD-6500 just means it's an Ultegra 9-speed rear derailleur. Longer cage indicates GS model (triple), shorter cage SS (double). You can find pictures of the current RD-6600 (10-speed Ultegra) on Shimano's website for reference; the new derailleurs look almost identical to the old ones. At least enough to tell whether yours is the long one or the short one.