There's a lot, but one that's standing out in my mind right now is Garchomp.
Garchomp has a very intimidating design overall, which, I feel, is very suitable for a Pokémon like this one. If I were to meet a big dragon in real life, I'd likely keep myself away for a while until we're more familiar with each other and whatnot, as they could likely be dangerous, in some way, and having a cute or approachable look probably would not help in that regard. Really fond of what they did here, all-in-all.
In terms of battling, it could generally be quite an assist. Its Attack is pretty high, and so is its Speed. To top it all off, it's got access to some decent moves as well, such as Swords Dance, Crunch, Dragon Claw, Earthquake, and so forth, and with those, it becomes a lot easy when utilizing. Have used it plenty of times before, personally, and it's always been able to live up to expectations.
Due to similar reasons as above, I'm also pretty fond of Haxorus; it's got fierce look, and also some decent battling skills. Few others would be Dragonite, Hydreigon, and Flygon.