Amazon previews the Kindle eReader for iPad and tablets
Font size and background color are customizable, and there's a slick new page-turning animation (so you know you're reading a book, I guess). The real question isn't whether Kindle looks good, though, it's whether Apple will allow a competitor to its free iBooks app. I think Kindle shouldn't have any problem getting approved, though, because Apple has already approved the iPhone version, and they shouldn't give the impression that the approval standards are any different for the iPad.
Whatever happens with Apple and the App Store, Amazon was smart to build the app to be used on other tablet devices, too. If you're going to run a proprietary eBook store, you might as well run it on as many platforms as possible.