Reviews of several mobile media tools — Missouri School of Journalism Donald W. Reynolds Journalism Institute Mobile Journalism Tools Reviewed. Includes audio editing, file transmission, note-taking, geo-location, live-streaming, micro-reporting, and video and photo editing apps. Probably out of date the minute it was published, but useful. Most are cheap; less than $10, often a lot less.
Soundslides – free and low cost versions, for matching sound to still images. You get what you pay for — pretty good, though limited.
iMovie – works pretty well for matching sound to still images and video. More flexible than Soundslides.