SlideShark is a free app that allows you to view Powerpoint presentations on an iPad. After downloading the app to your iPad, you then register for an account at www.slideshark.com. You can then upload Powerpoint presentations from your computer into your SlideShark account, and then view them within the iPad app. Currently, users are given 100 MB of space for free. All animations, fonts, graphics, and colors are preserved when converted to the iPad format. To advance slides, all you have to do is tap or swipe.
If you are lucky enough to have an iPad 2 and a dongle, you can project presentations to large groups from your iPad without having to lug around your laptop.