Autoppt
Upload your slides or documents and get AI-designed slides based on it. This might be worth trying, at least for inspiration on slides if you're having trouble coming up with something more interesting than bullet points.
authorSTREAM Online PowerPoint Presentations and Slideshow Sharing
Similar to Slideshare, this site lets you upload PowerPoint presentations for online sharing. However, this site also allows conversion to Flash while keeping all transitions and animations.
Presentation Zen How to Design & Deliver Presentations Like a Pro (pdf)
Basic concepts for using PowerPoint effectively for delivering presentations, using multimedia learning principles from Richard Mayer. Includes a list of selected readings and example slides.
New evidence that bullet-points don’t work : Speaking about Presenting
Research applying cognitive load theory to slide presentations providing evidence that slides crammed full of text aren't effective for helping people learn and remember
Best Practices for Effective PowerPoint Presentations Assessment | Think Outside The Slide
A lengthy and thorough checklist for effective PowerPoint presentations. Although the list is set up by asking if you "not often" or "almost always" follow the best practices in general, you could easily adapt this as a checklist for reviewing a specific presentation.