I have an NZXT PP-800
It's been fine for two years now, but if I ever want to say do a Crossfire with it I want to make sure it won't like explode on me. I say this because of threads I've seen on other forums where the OP apparently had their PSU burst into sparks and ruin their systems.
It hasn't been certified by AMD/ATI for Crossfire.
However, it has four +12V rails, rated at 18/18/20/22A. (That's 78A total, which means that you can't draw the maximum from all of the rails at the same time.) It has two 6+2 pin and two 6 pin PCI-E power connectors.
That may not be enough for two Radeon 6990s (more than 300W each), but it ought to be adequate for two Radeons of most other types.
I have no personal experience with that power supply, but a quick look at the reviews online suggest that it's not a poor one.
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