Update: Apple seems to have temporarily pulled this update in order to fix widely-reported crashes. It will likely be available again soon.
Update 2: It’s back now.
Apple has pushed out an updated version of iMovie for iOS (version 2.1) today that features support for the newly-released iOS 8 software and several other new features. The update includes 10 new Apple-designed filters that can be applied to your clips, speed settings for projects on newer iOS devices (iPhone 5s, iPad Air, and Retina iPad mini), as well as iCloud Drive support.
You can also now export your videos to other apps using iOS 8’s inter-app connectivity features. An iMovie extension for the Photos application allows you to enhance the videos in your camera roll without leaving the app. Titles can now be created with bi-directional text, and support for five languages has been added.