I have some Kindle made books that I'd like to get to be seen through my iPad's Kindle app. How do I do this?
1. Like the others already said, use the Archive feature for books that you purchased in the Kindle store.
2. Send the document to your Kindle eMail address: <YourAddress>@kindle.com -- Amazon will then convert the file for you and add it to your Kindle archive. They -- might -- charge you a fee for that service.
3. Adding eBooks directly to your device only works with a real Kindle, but NOT with the Kindle app. With the Kindle app, you only have options 1 and 2.
If you have eBooks from other sources than Amazon and do not want to use their conversion service, you can either use Apple's iBooks (which supports ePub format) or Stanza as your eBook reader. To convert eBooks from various different sources to various different target formats, you can use the Open Source software Calibre -- it can even convert PDFs to Mobi or ePub format. Works great!