A newly redesigned $100 note goes into circulation on October 8.  The new design was announced several years ago, but production delays at the Bureau of Engraving and Printing have slowed the bill's introduction.

The new $100 note indcludes two significant new security features:
A blue security strip through the middle of the bill and a larger inkwell and Liberty Bell watermark.

This video from the Federal Reserve Board explains the changes and shows off the new Franklin.