I just had an idea up and hit me about the head. I think its so stupidly simple, it might be a good idea...
A "rollover" on power attack. You don't take any kind of minus to hit with power attack. You make your attack rolls as normal. The amount you exceed the opponent's AC by is added to your damage roll. For two-handed weapons, you add double the value you exceed the opponent's AC to damage. The extra damage can't exceed your BAB (or double your BAB for two-handed weapons).
Fighter types would no longer have to fuss and guess over what to reduce their to-hit by to add to damage - the calculation would be automatic. Should go a tad bit faster.
I thought about this a couple of times - not for power attack, but for D&D in general. I was thinking about alternatives to attack and damage rolls, so instead of rolling for damage, you'd just deal whatever is left over from the attack roll.
The problem here is that you'd either have to tell the players what the AC is (though since there's no more power attack, it wouldn't do them as much good any more - but still, it's one of the things I like players to find out) or do the calculations yourself. Players would have to tell you what they rolled all the time - they might already, but in our games, when the players start homing in on the AC, they won't aks whether they hit when their result was better than a previous hit or worse than a previous miss. It speeds up things a bit, and is more convenient.