Oh, of some note here too, I was a perfect victim in high school. I was one of those guys who sat and read books during my free time at school, didn't fit in particularly well and most notably I couldn't for the life of me push my weight past 130lbs. (Apparently all my wishes for weight gain at that age were granted some 5 or 10 years later...)

It is a shame that this story is all too common. Kids should not be the ones who have to deal with bullies. Teachers and parents should be taking care of it for them.
I do understand that it is true that many times these solutions don't fix things.
Once these options are exhausted, retaliation is the only answer.
No one likes to be the victim of abuse. Most of the time, once one bully gets hurt, the game is over, and they will pick on someone else.
It seems some kids at your school were not too bright, and didn't get the message. Their loss.

Sifu Crake

The bes way to tackle a bully(in a physical manner) would be to go all out, use aggression, and attack weakpoints. Keywords are speed AGrssion and surprise Don't stop util you feel he/she has learnt his/her lesson.

ps. Only do this in the face of dire need, fighting should always be the last resort.