In terms of easy bosses, that would have to be versing guilty spark at the end of halo 3, also that ADD guy from Bully. In terms of hard bosses, that creepy ass clown bloke from Dead rising. He was hard as hell, there are zombies everywhere and I had a good case of the jibblies after that disturbing intro-cutscene. A little off topic but in terms of clever boss-fights I'd have to say Glad0s from Portal (I loved that game), just about every boss-stage in Bully (Especially the nerds and the greaser boss stages), and that Locust leader from Gears of War 1 (As you can see I'm both a microsoft lover *Not a fighter* and a near amnesiatic)