Alternatives to PowerPoint

I don't make presentations very often, in fact I only made two serious ones, but for one I used Powerpoint and for the other I used Impress. Actually I didn't feel they were too different, but I only needed basic features in my presentations - I didn't use animations and things like that, I just pasted text and pictures there. I guess I'd notice more differences if I needed the more advanced features.

OpenOffice.org give you everything and anything you could possibly want to use in a reasonable presentation. It's very easy to use too. Perhaps even easier than PowerPoint. However, some of the best presentations I've seen didn't use PowerPoint and some of the better ones use a PDF.