A term used only by Caucasians to describe something awesome. When someone white wants to sound like a "gangster" they will add for-shizzle to the end of a sentence.
Fo' shizzle ma' nizzle" is a bastardization of "fo' sheezy mah neezy" which is a bastardization of "for sure mah nigga" which is a bastardization of "I concur with you whole-heartedly my African American brother"