SlideRocket is a web application that provides everything you need to design professional quality presentations, manage and share libraries of slides and assets, and to deliver presentations in person or remotely over the web.
I've played around with it for only few minutes, but it looked fantastic! Just using one of the default themes, I could create a presentation that looks much more professional and beautiful than when I used, let's say, a MS PowerPoint. It seems to be very feature-rich, yet intuitively designed as well so that it is easy to learn and use. When I need to prepare a presentation for my church activities (or else), I am going to try this one out for sure.
If you want to try it for yourself, you will need to request for an account since it isn't fully released yet, but in a private beta phase.