My wonderful, wonderful friend Ampharos.
Ampharos is an incredible Pokemon that has helped me countless times in HeartGold and SoulSilver, and I don't think it would be any different in Crystal ten years before.
It's only available in Gold and Silver unfortunately, if you have the games Flaaffy is available on Routes 42 and 43.
If you don't have the game, you can try Jolteon. I mean, your name is Eeveelution. I think you might want it. xD
Of course, if you don't want another Eeveelution on your team, I understand. :3
If you don't mind, you can get it from Bill. Or, you can breed your Espeon and Thunderstone and blah blah blah.
You can also use an Electabuzz, available at Route 10 in Kanto though. (I know, these aren't very helpful suggestions xD)
However, you WILL need a Flying type. Skarmory (Route 45, great for the league), Crobat (like, anywhere cave with Zubat xD, also good), Dragonite (Dragon's Cave, takes a while to train though) and, the classic Pidgeot are all very helpful. Seriously!
Okay, hope I helped. :)