How can I view PowerPoint files on an iPad? I want to play PowerPoint presentations on an iPad which I create on a computer, using MS Powerpoint 2010.

I know there is an Apple app for that, but it isn't free. So, are there any other apps or methods?
If you have only small amount of presentations, which you want to play on iPad, you can convert pptx file into jpg's or pdf's on PC and then upload it to iPad