Serious answer:
Combat reflexes
Spiked chain
Very high strength
Rage (to bump up strength)
Improved Trip
Large size (from Enlarge person spell or other source)
Mobility
Spring Attack
Whirlwind Attack
Consider a 10th-level barbarian with a normal Str of 20, under an enlarge person, bull's strength, and raging. We're now talking a str of 30, I believe. The barbarian's trip bonus is +10 (str) +4 (Improved Trip) +2 (spiked chain) +4 (size), for +20 total. He can whirlwind attack everyone out to a range of 15' (due to enlarge person). Each person that fails their opposed str/dex check against him suffers an additional attack as he tries to hit them, gaining at least +23 on his attack (+10 BAB, +10 Str, +4 prone, -1 size). When they try to stand up, he gets an AoO on them at the same attack bonus. Each attack does at least 2d6+15 damage (large two-handed weapon).
If the spiked chain is masterwork or magical, of course, then things start to get nasty.
Daniel