If your DM allows variant/ACF chaining, you can get relentless smash (Dragon 349, p92) on a rage cleric (Dragon 333, p86). Relentless smash allows you to stun an opponent for 1d3 rounds with no save, but you have to either score a critical hit or hit him three times in a single round. It replaces mighty rage at 20th level. Rage cleric gets rage and its associated abilities, including mighty rage at 20th level. The main things you give up are turn undead and domains, also the ability to be lawful and proficiency with medium and heavy armor.
Okay, so you give up some nice stuff, don't get the payoff until 20th level, and are stuck single-classed until then, but … I think I just turned myself off of the concept. I'm posting this anyway.