I'm good thanks.

Now I am fully aware of the idea that, “I’m well” could in fact be the proper response to the question, “How are you?” As opposed to the more commonly used, “I’m good.” Though, like most others I have for as long as I can remember, been in the habit of saying, “I’m good.”
I am also fully aware that many nitpickers out there have chosen this little language discrepancy as their pet peeve. Well grammar snobs, your pet peeve has become my pet peeve. I find it so obnoxious when I respond to the friendly greeting with a perfectly polite, “I’m good thanks, how are you?” Only to receive an, “I’m well.” with an air of disapproval and an incredibly facetious annunciation added to the, well. Or even worse, some smartass remark on my incorrect use of the English language.
This used to make me feel bad and for some time I made an effort to say, “I’m well.” But old habits are hard to break and I kept reverting back to, “I’m good.” After a while, feeling inferior to the grammar gods turned into a certain anger towards the grammar gods and I just began to say, “I’m good.” in knowing defiance as opposed to by ignorance or habit.
Being the total nerd that I am, I did some Google searching today in an attempt better understand the facts behind the argument and low and behold I found my justification.

“Even though good is primarily an adjective, it is OK to say, "I am good": am is a linking verb, and you use adjectives after linking verbs. Most sources say well is reserved to mean “healthy” when it's used in this way. So if you are recovering from a long illness and someone is inquiring about your health, it's appropriate to say, “I am well,” but if you're just describing yourself on a generally good day and nobody's asking specifically about your health, a more appropriate response is, “I am good.”

Now if only I can memorize that last paragraph and recite it to the next pretentious shithead that tries to make me feel stupid for telling them, “I’m good.”

Reference;

Grammar.com
Yahoo Answers
Merriam-Webster