Over at BlenderGuru they have a nice tutorial on how to create a fireball explosion with Blender.
You guys have been asking for this for quite sometime now so I decided to finally deliver on that request. Think of it like an early Christmas present (that explodes in your face).
The particle effects look a bit cheesy, but the fireball is first-rate. Check it out.
How to Create an Explosion from Andrew Price on Vimeo.
via How to Create an Explosion | Blender Simulations | Blender Guru.