One sort of silly idea is to "keep" Improved and Greater TWF, and simply have them give you even more attacks on a full attack, or two strikes as a standard action.

Improved Two Weapon Fighting
Prerequisite: Two Weapon Fighting, Dex 17
When you make an attack action as a standard action, an attack of opportunity, or at the end of a charge, and are wielding two weapons, you may attack with each of them once at your highest base attack bonus if you take the two-weapon fighting attack roll penalties.


Greater Two Weapon Fighting
Prerequisite: Two Weapon Fighting, Dex 17, BaB +6
When you make a full attack while wielding two weapons, you can make an extra attack with each at your highest base attack bonus in addition to any attacks you would normally make. This stacks with any similar effect.