Paid apps on iTunes are sometimes offered FREE temporarily. One app that is currently FREE as of this writing is ComicStrip–CS. It has earned 4.5 stars on iTunes with 261 ratings, so that’s a good track record.
It’s meant to be an app for creating your own comic strip, but you can also use it to create photo montages like this one (all photos in this montage taken by my son Nick with his iPhone). The only feature I’d like to see added is the ability to change the font size. The word bubble does automatically resize to the amount of text you write.
Hint: To change the position of the word bubble “tail”, just drag it with your finger.