Ok guys, I reduced my massive scene file for this shot down from 30 megs to 90k by just including the meteors and the associated shader.

Feel free to use/edit it to learn from.

The shot was portaying 2 meteors falling from the sky in front of a moving camera and smashing into a few buildings.

I basicly started off with 2 simple omni emitters parented to animated spheres.
I adjusted the emitters to only emit software cloud particles for about 3 seconds of life with a bit of variation.
The spheres had their Primary visibility off, as they were just used to animate the emitters.
I added one or two expressions on the particle shape to give some scale over time, and some death randomness.
(its been a while, so just check out the particle shape to see what I did )

The shader was based on a lava shader that I made that contains a 3d fractal and a Stucco node.
The For this scene I animated the X-translation of the 2 3dtexture placement nodes to give it some "seethe" or "convolve" to make it look like the fire-cloud was rolling and had a sense of thickness or volume.

Then quite simply, I rendered the trails in Mental Ray as separate passes, and in my compositor I adjusted the color a bit more and added a subtle animated VERY low noise displacement to the plates to give a little more sense of roll or convolve.

The color adjustments I made were pretty simple.
I adjusted the levels a bit to bring out the black/darker color.
I also sampled the red and oranges to overlay back on top of themselves to over-accent the dark colors giving more thickness to the trails themselves, and that also gave me more control over the bright red/orange gain so they wouldn't blow-out and seem too bright and "glowy".

Then I comped that all together overtop of the other plates and the natural life transparency Vramp in the shader allowed for a good blend with the shot.

Here is the scene file.
Feel free to ask any questions, but remember, your shots WILL be different, so you MUST remember that particles and dynamic simulations are usualy trial and error, so SAVE OFTEN and save MANY variations so you can go back to the beginning if need be

Good luck!

NOTE: This is a Maya 8.5 file