Get all the flags,feathers,glyphs and property (safehouses filled aswell)
With the flags you get a cape making you immune to notority which as far as I remember is the same for the buying all property cape.
Feathers I cant remember what you get for that probably just a trophy as they are easy to find.
Glyphs get a secret something
Think the hardest thing is the flags ... trying to find them in the romulas places was the worst
FEATHERS? U GET NOTHING! in AC2 after getting all feathers ezio's mom gets up and gives him a hug. awe:}