Everyone's going to answer Flareon, but his problem isn't the lack of moves. It's the fact he's outclassed in most roles.
Giving him the Arcanine treatment (Outrage, Wild Charge, Close Combat, Crunch, and of course Flare Blitz) would help him tremendously, but at the end of the day he's still got only 65 base Speed and is quite easy to kill despite having monstrous Sp.Def. He would be better than Rapidash and Heatmor, but those suck anyway and no one uses them.
That being said... IMO Glaceon has it even worse. Mono-Ice is a poor type. He has good defenses but only one resistance. He's a Special sweeper with no Speed and no moves other than Ice Beam and Shadow Ball. A recipe for disaster.
Truth is all Eeveelutions suck one way or another in battle and the only usable ones are those with good abilities or those which can use well the support moves Eevee gets. Vaporeon fits both criteria. But I think Vaporeon is boring, ha ha. :D