While there are a number of office suite type of applications for the iPad, your first port of call should be to check out the applications provided by Apple. There is Keynote for the presentations as well as an excellent app in Pages for your word processing. Mind you for working with text I do actually prefer to use Nebulous Notes and only use Pages for something that I think I might want to print at a later stage.
When I looked into using Keynote for iPad I was actually quite impressed with the number of Keynote template or themes that were available. There are even quite a large number of transitions available within the iPad Keynote app for transitioning from one slide to the next. You even have the Magic Move for doing something fancy with an image that needs to change size and position in between Keynote slides.
While there may be other applications that you can use to create PowerPoint presentations on your iPad, if you use Keynote and iCloud, you can go to the iCloud web page and download a PowerPoint file that you can use on another system.
