In the past few years, I've used a Nikon Coolpix 5000 and a Canon
Digital Rebel, and neither has been very good at taking pictures
outdoors in the low light conditions of a Northwest Winter.

Just wondering if anyone is aware of any models of "prosumer" level
digital cameras (in the $400 to $800 range) that are known to be
exceptions to this rule?  As of right now the only one I have heard of
is the Sony DSC-F828.
Thank you.

Look into the new Minolta D7.
Ease of operation with terrific results under every lighting condition
I've put it through.
It'll cost you towards the upper end of your price range, plus getting
a lens for it.
Good luck with your search.