combustion also accepts After Effects plugins, there are a number of them that have similar effects to the Sapphire or 5D sparks. Although combustion can use Photoshop plugins, these aren't recommended since they're not designed for animation.
A few good sites for plugins:
The Foundry - www.thefoundry.co.uk
Boris FX - www.borisfx.com
Digieffects - www.digieffects.com
Re:Vision FX - www.revisionfx.com
You should also check the compatibility list found in the combustion Release Notes PDF to make sure the plugins you're interested in are supported.
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Greg Niles
combustion Product Specialist
Discreet