I don't know if someone made something similar before, but I created a sort of a duel with spells on Photoshop CS4, and I wanted to share. It is something horribly simple and rough, but you can move the green one (similar to the Avada Kedavra) and a part of the white one (a sort of Protego), to match with the wands of your protagonists, so that you can simulate a duel.
Three layers: green, whitebig and white little.
I hope someone will like this... I mean, I looked for something similar on internet for ages, to create my wizarding scene, but found nothing premade... So I decided to put online my results. Hope you enjoy and use.
In the preview, you can see my friend and me!
I used different brushes to create this effect, and I swear that I'll credit everyone asap.