What are the different types of justifiable force according to the law in list form?

Laws rarely spell out in black and white what you can and cannot do.
Justifiable force is typically relative to the situation and the
perception of the person who uses it. Texas law says:

Conduct is justified if.
(1) the actor reasonably believes the conduct is immediately necessary
to avoid imminent harm;
(2) the desirability and urgency of avoiding the harm clearly
outweigh, according to ordinary standards of reasonableness, the harm
sought to be prevented by the law proscribing the conduct; and
(3) a legislative purpose to exclude the justification claimed for the
conduct does not otherwise plainly appear.
http://www.texaspolicecentral.com/title_2.htm#9.02%20Justification%20as%20a%20defense

An absurd hypothetical case would be me shooting someone who was
threatening me with a snail. If I genuinely believed that the snail
was a deadly weapon, then the law might excuse my actions (though I
doubt any jury would).

It is going to vary by state.  In contrast to the Texas law cited
above, New York State law requires you to take every possible action
to exit the area before you take defensive action.

"the actor may not use deadly physical force if he knows that he can
with complete safety as to himself and others avoid the necessity of
so doing by retreating;"

From NY State Penal Cdde, Section 35
http://ourworld.compuserve.com/homepages/Jacob_J_Rieper/pls35.htm

You may be thinking of the "justification defense". 
According to Black's Law Dictionary,7th edition,  "Traditionally the
following defenses were justifications: consent,self-defense, defense
of others, defense of property, necessity(choice of evils), the use of
force to make an arrest, and the use of force by public authority."