You can use brute force to slam into and knock down your enemies.
Prerequisites: Improved Bull Rush, rage ability, size Large or larger (goliaths qualify by virtue of their powerful build racial trait).
Benefit: While in a rage, you can attempt to knock down any creature that you successfully bull rush (that is, that you push back at least 5 feet with a bull rush attempt). You take a –4 penalty on your Strength check to bull rush the opponent, but if you win, the opponent is knocked prone at the end of the bull rush.
Source: Races of Stone, page 143.