Sometimes the best presentation is... no presentation. Ditch the slides completely. Put the projector in the closet, roll the screen back up, and turn the damn lights back on!
... But given how many people hate slide presentations, why is it universally assumed that where there is "a talk", there's PowerPoint (or its much cooler cousin, Apple's KeyNote)? Conference coordinators rarely ask speakers if they'll be projecting slides. They send out the slide templates, then start demanding your slides several weeks before the show. Saying you don't have slides is like saying you'll give your talk naked. "You mean... you're going out there with nothing???"
I too am puzzled by the ubiquitous presence of slides. Those who speak for a living, teachers, lawyers, preachers, never use slides. Surely there is a lesson there.