I really love Bronzor and Bronzong, personally. They might not be as popular among fans, but I find myself enjoy their appearance quite a bit--to me, it's quite intriguing to see a real, living bell--and while battling, they're also pretty good. They've got enough bulk to endure hits, and while doing so, they could set up some entry hazards as well. That, if you ask me, does lend a hand when it comes to damaging opponents.
My second vote has to go towards Metagross line. I've been a fan of it ever since I was introduced to this Pokémon in generation three of games, and still am. Its color-scheme is marvelous, and body structure, overall, is simply stunning. As for third, that's got to be Skarmory.