A lot of Apple's "iApps" have a standard mechanism for browsing media (photos, music, movies). In iMovie HD, for example, click the "Photos" tab to observe the media browser for photos. In Pages, click the "Media" toolbar item to observe the media browser for photos, movies, and music. Or in iTunes, click the slideshow button then the Music button to observe the media browser for music.
It would be great if this was a public framework that we could access. Apparently there was a private framework, but it doesn't seem to work anymore — not to mention that we're not supposed to use private frameworks.
Apparently, Comic Life just wrote their own by parsing Apple's XML files. OK, so you can do that. But it's a hassle. It would be nice for Apple to provide a standard way to access media, so that developers don't have to keep inventing the wheel.
Of course, I submitted this request to Apple (Radar ID 4263260). Fellow developers, if you think a media browser would be a nice public API, please submit this request as well!