Improved Unarmed Strike

Type: General, Fighter
Source: Player's Handbook

You are skilled at fighting while unarmed.
Benefit: You are considered to be armed even when unarmed - that is, armed opponents do not get attacks of opportunity when you attack them while unarmed. However, you still get an opportunity attack against any opponent who makes an unarmed attack on you.
In addition, your unarmed strikes can deal lethal or nonlethal damage, at your option.
Special: A monk fighting unarmed automatically gains the benefit of this feat.
Normal: Without this feat, you are considered unarmed when attacking with an unarmed strike, and you can deal only nonlethal damage with such an attack.