There are many Pokemon I can think of, but I'll go with Excadrill at the moment.
Excadrill @Air Balloon
Nature - Jolly
Ability - Mold Breaker
Spread - 252Atk / 252Spe / 4HP
This set sent Excadrill straight up to Ubers. After one Swords Dance, Excadrill OHKOs Golem straight through it's Sturdy. Here is the damage calc:
+2 252 Atk Mold Breaker Excadrill Earthquake vs. 0 HP / 252 Def Golem: 440-522 (146.1 - 173.4%) -- guaranteed OHKO
Otherwise here are some other damage calcs of Pokemon with no boosts:
Basculin: 0+ SpA Choice Specs Basculin Hydro Pump vs. 0 HP / 4 SpD Golem: 916-1080 (304.3 - 358.8%) -- guaranteed OHKO
Haxorus: 252+ Atk Choice Band Mold Breaker Haxorus Earthquake vs. 0 HP / 252 Def Golem: 260-306 (86.3 - 101.6%) -- 12.5% chance to OHKO
If you wanna go with something really cheap though, Haxorus also get's Guillotine, and if that hits, Golem's out of the game.
Hope I helped!