OC/CS/CN combo spray
stun gun
expanding baton
*check your state laws. Some states have banned some or all of the above for civilian use
Also note, it helps if you're trained to use these.. particularly the baton, else it may be more dangerous for you to try to use it.
I don't usually carry less than lethal alternatives unless I'm at work, where we use them for crowd control. If you're afraid of killing someone, shoot them in the knee.