You don't hear much about web apps these days, but there are some that look and function so well you might forget you're using Safari. Google has been constantly improving its Gmail web interface and they've recently revamped the mobile site again. Similar to the native Apple Mail app, the mobile version of Gmail's website is designed with the iPhone touch screen in mind.
You can swipe to archive a message, and now Google has improved the scroll speed to simulate the same quick flick of the finger to jump down in the mailbox. The toolbar has been anchored to the top of the screen, a welcome reversal of a recent change that had the toolbar floating over emails.