HelloSlide is a pdf-only tool that allows you to add computer-generated voice to your documents. Upload your presentation, type the speech for each slide, and the programs automatically generates audio. Presentations are searchable, editable, and available in 20 different languages. An edit feature allows you to tweak the speech without re-recording the audio. Translations are available as a paid feature. This may be useful for ESL learners. (Note: it is super easy to export PowerPoint and Keynote files as pdfs.)
Empressr is a rich media presentation tool where you can tell your story anyway you like. Add photos, music, video, and audio, and share it publicly or privately. Post a link or embed your presentation. Empressr also has great charting and table tools.