Yeah, I'm a bona-fide space geek and proud of it, so I was thrilled to hear that the official NASA iPhone app [iTunes Link] is now available free of charge. The app was created by the New Media Team at NASA Ames Research Center, and for their first app it's surprisingly robust, bug-free and full of features.
The front screen of the app provides a window into current and future NASA missions. Along the bottom of the display are buttons for missions, images, videos, and updates. The updates are fairly current -- there were 11 posts about various Earth and space missions today alone -- and often include links to videos.
I found that the app worked best when I was downloading the videos over Wi-Fi, so be sure to keep that in mind if you're trying to get watch a launch video while on 3G service. Check out the gallery below for screenshots from the app.