you can use a one handed weapon 1 size larger as a two handed weapon.
I don't have the books at hand but I think that something like 1d8 would be about the best you can do
This feat allows a large melee weapon (such as a Greatsword) to be wielded in one hand.
Prerequisite: Str 13, +1 Base Attack Bonus.
Benefit: This feat grants the ability to wield melee weapons that are normally two-handed for your race with only one hand at a –2 penalty to hit.
Special: A Fighter may select this as a bonus feat.
My ruling using this and my interpretation of RAI allows you to, essentially, move up one size category with all weapons. I have used this in the past a few times to make two-handed users into pretty beastly damage dealers when they hit. I would talk with your GM first on it, though, because their interpretation may be vastly different than mine.
Also, I allow alot of stuff from 3.x to just carry over, because, well, it was fun and not game breaking, so check on that too...
i really love the monkey grip feat and wished it had been reprinted in pathfinder so i wouldn't have to ask to use it. but i think my DM wouldn't have a problem with it.
How about an empathic "no", because no-brainer feats aren't good design. Also, making the gap between 2h weapons and every other combat style isn't good design either.
Switch Hitter Ranger using Falchion level 10 Favored enemy factored in.
63.09 DPR normal sized weapon
Monkey Grip in place of weapon focus deadly aim DPR 64.60
So damage went up by 1.6 in that case.
Switch Hitter Ranger using Falchion level 10 not using Favored enemy
31.26 DPR normal sized weapon
Monkey Grip in place of weapon focus deadly aim DPR 29.68
Without the ranger's favored enemy bonus to offset the penalty Monkey Grip is worse by about 1.5.
PS:I was power attacking in all cases. It seems that you can can offset the -2 to hit that it might be worth it, but if not then Monkey Grip is indeed a paper trap.