Cool tool: PPT Minimizer
I get a lot of big Power Point files at work. They contain large images/screen shots which has been resized to fit in the slides but Power Point stores the high quality image which occupies a lot of space.
PPTminimizer reduces PowerPoint presentations by up to 96% of their initial size in seconds by optimizing graphics and embedded objects.
My favorite feature is the Microsoft Outlook plugin that can automatically optimize Power Point attachments when you send mails.