Photo Peach provides an easy way to create slideshows from pictures.
Once registered, simply upload your photos, choose some music and you will have a slideshow!
See this example on Year 7 thoughts on learning journals.
Prezi allows you to create dynamic presentations which provide an overview and allow you to zoom in on any element. There are no individual slides, you work on a large canvas on which you can zoom in and out. You can create a path to show parts of your canvas in a particular order. Learn Prezi.
Slideshare is a site which allows users to upload slideshows, it is also possible to upload documents. Several formats are acceptable:
Presentations: pdf, ppt, pps, pptx, ppsx, pot, potx (Powerpoint); odp (OpenOffice); key, zip (Apple Keynote).
Documents: pdf, doc, docx, rtf, xls (MSOffice); odt, ods(OpenOffice); Apple iWork Pages.
(Note that this site is intended for users 18 and over but will accept students age over 13 with parental permisson). The presentations from SlideShare can be embedded easily into a blog or website.