Some monsters OTOH, could have very different weapons, like a poisonous bite and non-poisonous (but maybe with higher damage) claws. Still, I don't see a very important reason why these couldn't just be used in separate rounds.
Let's take a giant scorpion, for example. I don't have access to the real stats, but let's say under the current rules it gets two claw attacks at +3 to hit (1d4 damage each) and a tail sting at +1 to hit (1d4 damage + poison).
Pesonally, I'd like to see this turned into one attack at +5 to hit that deals 1d12 damage + poison. The +2 bonus comes from treating the additional attacks as "assist other" sort of bonus and the poison save takes care of determining whether the tail "hit". The 1d12 damage accounts for the fact that from one to three of the attacks could hit, so you get the whole damage range in one go.
If our scorpion needed to attack more than one foe, we could give it a special attack/stunt:
multiattack: The scorpion can attack up to 3 targets at +3 to hit, dealing 1d4 damage. It may nominate one of the attacks to be poisonous (before rolling the attack).
Now, granted, that is a simple attack, but it shouldn't be too hard to do something similar to other monsters - even dragons or sweep attacks from a giant's club.
And what about the fighter and his multiple attacks? Instead of granting an extra attack, give the fighter a +1 or +2 bonus to hit and just bump the damage up by 1d6 to account for the extra swings.
Finally, what about the two weapon fighters - say someone with a longsword (d8) and dagger (d4)? Simple - one attack at +2 to hit that deals 1d12 damage, add Strength bonus once. Two longsword? Well, that'd be little trickier - got a d16 or an easy method to equate one?
