Really, I'm not sure how cool they are, and some of those listed weren't actually from Happy Meals (which were not introduced until 1979), but I do like the little McDonald's restaurant replica (from pre-Happy Meal 1969), that is kind of cool.
The 50 Coolest Happy Meal Toys of All Time
Does anyone reading this collect these, by the way. I knew a guy who had a pile of his old Happy Meal toys and he really believed he'd make a killing on them. I think he ended up losing them all during a move.