You noticed, perhaps, that I am not using ppt. I find it confining, rigidly serial, and not inherently interactive. Blogs on the other hand are read online with hyperlinks active, easy to scroll through postings (the equivalent of ppt slides), have built-in comment functionality, provide built-in RSS feeding, and invite linking with other sites.
These features of blogs promote engagement, interactivity, reflection, review, commentary, linking to examples -- all qualities of active learning!
Having written that, the linked site is one from the University of Minnesota about how one can make ppt a tool for active learning!