Put this in the category of "I didn't think I could do this on my iPhone." Cinefy is a US$0.99 app for the iPhone that lets you overlay Hollywood-type special effects over your videos. There are dinosaurs, missile attacks and lightning strikes among 100 nicely rendered CGI effects. The app also allows you to add a music track from your iTunes library.
The app is timeline-based and easy to figure out if you have done elementary media editing, but it lacks built-in help. It would be nice if there was a demo video so a novice could figure out the basics.
You have to layer the effects over a video clip, but developer Daniel Hellerman told me that an upcoming version will support photos. If you want to have the most realistic effect, shoot the background with a steady hand. When you're done, you can send the finished clip to your camera roll, and email it or send to your favorite sharing service.
Cinefy is an amazing app. Some time ago I took a look at Action Movie FX, which is free and does similar things but has far fewer effects.
The app is a large download because of all the effects, so make sure you have the room for it. The developer is committed to adding features and keeping it updated. I really enjoyed playing with Cinefy, and there are lots of creative possibilities.
I've included a couple of screen grabs from movies I created. The movies have more impact than the stills.