I hesitate to calle iPhone optimized websites “applications”, but today, Google launched a fantastic looking interface for Safari mobile. Working with both the iPhone and iPod Touch, the search engine master has created an easy to use an intuitive interface that closely resembles the Facebook iPhone UI.
This is especially great for iPod Touch users, because its the first really great web based mail UI for the iPhone. If you haven’t checked it out yet, head over to Google and give it a look.
Not exactly an application but a good start (I doubt google will ever play in the eventual iphone apps game but rather stick with browser interfaces). I found some info on this here: https://personafile.com/iPhone-apps.html