I would try to collaborate with a classroom teacher on a unit lesson to have a content area to use with your Powerpoint lesson. If that's not possible, typically I ask the teacher to save student work composed in Word and we use the same paper for the Powerpoint presentation. We add images, record their voices, transition, add audio files from Freeplaymusic.com or Soundzabound.com. They can save a Wordle as a jpeg and add it to the PPT. Students can also create public service announcements (PSA)s on various issues; that would require research and may take more time.
I have my sixth graders use PP to create digital picture books around a curricular theme (last year was cellular mitosis). They use a familiar platform but in a way that allows them to be creative/.
I am a big fan of having students make cartoons with Powerpoint before they do anything with informational presentations. They will learn a ton about how PPT actually works as opposed to learning how to fit as much garbage as possible one on single slide.
I have used Death By Powerpoint by Alexi Kapterev. It can be found on Slideshare. The time spent covering this made a huge impact on the quality of student presentations. (Most presenters can benefit from watching this.) I plan on following up with lessons on searching for Creative Commons license images this year.
This dramaticly improves their presentations. The lack of words on the screen encourages students to use notes and not "read the slides." Pamela's advice to produce the paper or at least the talking points prior to working on Powerpoint is key.
I have each of my students make a "What Not To Do" slide for a PowerPoint project. They add too much text, loud colors, excessive animation, pixelated images, sound, etc... Its a fun and crazy way to emphasis proper PPT ettiquette by doing the opposite and leads to a good discussion on what to do and why. Plus it gives them the chance to "play" with the animations and then they don't feel compelled to use them with their regular PPTs.