The long rumored Google eBooks service appears to have gone live today... somewhat. The service allows you to not only read books on an iPhone, iPod touch, or iPad, but on the web or on Android phones, Nook, and Sony devices. The iOS webpage boasts over 8,000 titles already available for download.
The only problem right now is the fact that the native app isn't currently available for iPhone or iPad yet. (I'm getting the "The item you've requested is not currently available in the US Store" error but we'll update when that's sorted out.)