I must say Noctowl.
I think it is more useful than what it gets credit for. It got good stamina and defense. It can learn the psychic moves Extrasensory and Psychic witch makes it great for taking down fighting type Pokémon. And it's flying type levels out the normal types weakness for fighting (it does however get weakness against electric, rock and ice).
Another one I like is Tentacruel.
High defense and decent attack and stamina. Poison and water type has its advances and dis-advances. Since it have poison type it levels out the water type weakness to grass types (although it gains weakness against psychic and ground). However when putted against the right Pokémon it can take good abuse and put in a few nice hits as well.
And of course there are more that are useful as attackers. Pidgeot, Jynx, Lanturn, Skarmory, Piloswine, Porygon2, Omastar, Cloyster, Forretress and even one of my most hated Quagsire can be usefull with its water/ground type. Theese are just a few examples.