Iterative Attack = Extra Dice
The idea here is that where you would normally have iterative attacks, instead you do one attack and double the dice (on a full attack only). For instance:
Sword attack: +9/+4 to hit, 1d8+4 damage would become +9 to hit, 2d8+4 damage.
Bow attack: +11/+6/+1 to hit, 1d6+2 damage would become +11 to hit, 3d6+2 damage.
Potential Benefits: Less die rolling, bigger hits. Easier to penetrate DR even with smallish weapons. Crits become huge. Full BAB is a wonderful thing.
Potential Drawbacks: The ability to switch targets if you drop a foe with the first attack is lost. Attack becomes "all or nothing" because if you miss the first, you miss them all. Although crits are huge, there are fewer chances to get one. Less-than-full BAB can make you feel gimped.
Some Notes: The idea that only the dice multiply is to keep things roughly in balance with the fact that on iterative attacks, all attacks after the first are much less likely to it. Additional attacks, such as TWF, Rapid Shot, haste effects, are not included in this figuring.
Full Attack (with Penalty) As a Standard Action
Normally, a full attack requires a full action; this version would allow a full attack as a standard action but with a -4 penalty.
Potential Benefits: More movement, as you don't feel like your only chance of doing significant damage is if you can do a full attack, so you end up standing toe-to-toe with the monster and trading full attacks back and forth. Can be combined with the rule above in order to speed up combat.
Potential Drawbacks: Could be broken when combined with haste, TWF, etc., especially given the way BAB tends to outstrip AC. Do you want a fire giant running across the room and getting a full attack on you at +17 for 5d6+15? (Or +15, 5d6+22 with Power Attack?)
Edit: One more!
I'm also considering making crits automatically full damage with no confirmation (rather than double dice and mods).
Potential Benefits: Faster, crits happen more often, no trying to remember what damage doubles and what doesn't.
Potential Drawbacks: Crits become a flat number and may be a little less exciting. Players will end up taking more crits, too.
What do you think, sirs?