Yeah, tons. Apple has a Keynote app on the AppStore, it's $9.99 if I remember correctly. For simply viewing a .ppt file I prefer the Goodreader app, but you can't edit from there.
As for a free alternative, there's always Google docs.
Viewing Powerpoints on the iPad is a crapshoot. I have yet to see one not get butchered in the translation. Either the bullets are off, the fonts, and forget graphics. I have Goodreader and Quickoffice Pro. I am guessing it's the squabble between Microsoft and Apple, and Apple not feeling compelled to support anything Microsoft. Plenty of examples of this nonsense, with us users stuck in the middle.
The only way I have been able to view complete and accurate Powerpoint presentations on my iPad is converting them to pdf.
Hmm, interesting. My experience with Keynote has been pretty good. Granted, I'm not looking at very complicated .ppt documents.
The point about converting to PDF is good though. Goodreader lets you highlight and mark-up PDF files but not PowerPoint files. As a student, this is great for highlighting and starring the lecture notes provided by my professors. Instead of having to completely type out what he says (like most students with laptops) I simply swipe over a sentence and highlight it. Awesome.
I guess I'm just lucky that the majority of the computer labs on my campus have iMacs rather than Windows PC's. I can simply make a text document on my iPad using Pages and then download as a .doc file in the computer lab via iCloud. If you open an "iCloud .doc" on the PC version of Microsoft Word then it looks super messed up, but if you open it with the Office Mac version it looks totally normal. Zero formatting or compatibility issues.
I don't have Office Mac at home, but Pages export does the same thing. The problem is iCloud's "download as .doc" feature. Only use that if you're opening the file on a Mac and can do a "hard export." Hopefully that makes sense!