Something I think we forget, is that no matter how many attacks we get, only the first few are likely to hit a powerful enemy. So let's maximize the potency of that first strike, shall we?
Go with an orc, or some race with decent strength. At higher levels, after a few magic items, assume a strength of 30, so a +10 modifier. This won't end up being too important, except for the purposes of accuracy.
Class doesn't really matter, but you'll want plenty of feats. (So Fighter, maybe?)
You're going to want to invest in these feats:
Vital strike, improved, and greater
Improved called shot, and greater
Other than that, go crazy. You might want some feats or items that improve accuracy.
Pick up a colossal greatsword. The damage dice on this bad boy is 4d6. Have it be a +2 impact weapon, this ups the damage dice to 4d8. Enlarge person makes this 6d6. Finaly, the spell Lead Blades makes this 6d8. Now it gets fun.
Using greater vital strike, you get to roll your damage dice four times. This means you're rolling 24d8 plus whatever bonuses you have! The dice alone are an average of 120 damage, and plus reasonable strength bonuses (strength +10 mod, equals +15 dmg, and power attack another +15 dmg at lvl 16) this comes out to 150 average dmg per strike.
BUT WAIT, THERE'S MORE
Now you get to have fun with called shots. If your not familiar with how they work, you take a subtraction to your attack, but if you hit the targeted area, a bonus effect takes place. However, if you deal a number of hp equal to half their maximum, a REALLY bonusy effect takes place. (Hands are cut off, legs severed, etc.) The head effect, among some other combat penalties, is they fall unconcious for 1d10 rounds. This seems awesome, but it pales in comparison to heart shots, where THEY DIE ON THE SPOT.
But, since head shots are only -5, and heart shots are -10, we'll go for the head. If an enemy is low AC, though, go for the heart (of course).
So our damage was 150. Now, as long as the enemy's max hp wasn't 300 or more, they fall unconcious and you can coup de grace them.
If you want to go crazy with this build, dip into rogue to get some sneak attack dice. It doesn't stack for vital strike, but hey, dice are dice.