Dragon 301
Any Dodge bonuses granted to AC because of fighting defensively or Combat Expertise may be applied to a parry attempt's attack roll. For example, if a Swashbuckler takes a -2 penalty to his attack roll with Combat Expertise, he gains +2 AC and +2 to any parry attempts he makes.
Improved Parry gives one the option of a free sunder or a free attack.
Should parry attempts use up an AoO? Well, not if the user has to give up an attack on their round anyway.