We've covered a variety of light leak effects here from the free downloads right up to a hard disk full of 4K flashes, scratches and flares. CrumplePop have joined in with a package of over 43 1080p styles for $69.
Before we run the demo video, could this be the first product advertised that will work with FCPX? Brave, but we would guess that overlaid movies with a composite mode will work in the new version.
For $69 you get 7 Gigs worth of overlays and transitional light leak effects. Take a look at their sample light leak videos.