True there's a helpful answer already, but there are a couple of really popular and awesome fire types available at Mt. Pyre that haven't been mentioned yet.
I always liked it, it was just the coolest-yet-cutest-looking Pokemon to me.
Vulpix is found in the late 20s of levels and late 30s if you've got a "!" on your DexNav. It evolves relatively easily into Ninetales (Fire Stone), and gets some decent moves when you catch it. It even gets Flamethrower by default if you have a high-level DexNav-caught Vulpix. When Ninetales evolves, it'll get Nasty Plot from the Heartscale guy in Fallarbor town, and that'll just turn it into a death machine. I believe you find TM Dark Pulse in The Aqua/Magma hideout, and Ninetales will learn it. After getting both bikes and unlocking the Battle Resort you can get TM Energy Ball from the Safari Zone. If it has its hidden ability Drought, you can teach it an instant-activation SolarBeam. Any nature that raises Speed (except Jolly) is good.
My favorite Fire-type.
Growlithe, Vulpix' physical counterpart, will be available only after you have eight badges (DexNav detection only). It's also in Mt. Pyre and evolves the same way. You may want to wait until around level 41 before evolving so you can easily EV train by hordes. (using Heat Wave will help a lot - kill the leftovers that you miss with crunch) Growlithe has a great movepool - Outrage at Level 43, Flare Blitz at 45, Crunch at 39, and Wild Charge by TM. It will need Agility (Lvl. 30) to be sure it can outspeed whatever necessary. It also gets Intimidate, giving you some confidence in its Defense. Flash Fire is also an okay ability, allowing you to switch into expected fire moves unscathed. Any nature lowering Sp. Atk would do fine.