I had this on an old Palm and was a Beta tester and really love Astromist on the IPod Touch. It is better or comparable to the others I have tried, and I own most of the other higher end astronomy tools on the IPod touch. I love the way it works, and the enormous catalogs included. It is very customizable and allows you to turn on and off display feature easily, and has a great logging tool for observers. The ability to create custom lists has always been one of my favorite features.
TimmIPODTouch about Astromist