My husband created one that was brokenest - Fighter/Dervish with 18 attacks per round, 5 ft movement between attacks, and a crit chance of 12-20 on two scimitars, with a +4 to confirm crits. He one-rounded a dracolich...
Monks can get absolutely ludicrously stupid powerful if you get the right feats and the right items.
One that I made more or less ended up getting Monks banned (or severely limited) in my real-life group... my friend who was DMing at the time decided that I should just use average damage instead of rolling for when I hit with unarmed strikes to save time. However, it wasn't because of this that Monks were banned (as this can happen with just about any optimized melee character).
What really frustrated our DM was the fact that we didn't have anybody to disable traps... I'd just run through the area in question, setting everything off, and use my ultra-high saves to simply leap out of the way!
Feral Goliath (or half-ogre) Fighter with a Large Wounding Spiked chain, huge dex, and the feats Combat Reflexes, Combat Expertise, Improved Sunder, Improved Trip, Improved Grapple and Improved Disarm. Along with the combat progression for spiked chain. (Weapon focus etc)