Really cool way to create custom UITabBar for iPhone app?
Solution 1:
There's a project on github called BCTabBarController that aims to mimic the tab bar used in Twitter for iPhone. It's got some of the things you're looking for, and should give a great starting point.
Solution 2:
Both of these are good answers, but both libraries have problems: BCTabBarController doesn't know how to create the "blue" highlighted version of a tab bar icon; and iDevRecipies doesn't send events to child viewcontrollers nor resize the navigation bar on rotate.
Be warned: custom nav bars are a lot of trial-and-error debugging (as I have found).