Arcanine and Dragonite were probably the only two that I ever confused with being a legendary. I actually think both of them could qualify as one (Arcanine is referenced as one in the anime, and Dragonite has the pefect look for one), but I guess their availability factor takes that away (since you can have more than one from their pre-evolutions, where as usually with legendaries, there is only one available in the game).