There are quite a few but I will include two of my favorites.
Pyroar
Pyroar has a high Sp. Atk and more than decent Speed. Pyroar can outspeed Gourgiest and is unaffected by any of Gourgiest's Ghost type moves, most importantly Shadow Sneak. A Fire Blast from this guy, or even a Flamethrower for that matter, can do some serious damage.
252 SpA Choice Specs Pyroar Flamethrower vs. 252 HP / 0 SpD Gourgeist-Large: 494-584 (139.5 - 164.9%) -- guaranteed OHKO
Typhlosion
Typhlosion is quite the powerhouse. With the same Sp. Atk and slightly lower speed than Pyroar, Typhlosion can still easily outspeed Gourgeist. The benefits of using Typhlosion? Higher defenses and a better movepool than Pyroar.
Typhlosion can lose almost half of it's HP to a Shadow Sneak from Gourgeist, which is unlikely, and still OHKO with an Eruption.
252 SpA Typhlosion Eruption (82 BP) vs. 252 HP / 0 SpD Gourgeist-Large: 302-356 (85.3 - 100.5%) -- 6.3% chance to OHKO
Either of these are great choices.
