I'll start with my all-time favourite snow camouflage: Finnish M/05 snow camouflage.
It's such a great pattern... it's so effective at breaking up the outline. I had to recount to make sure there were only 5 soldiers (6 if you count the elbow of the one in the corner) in the above photo! I would love to get my hands on a set of this stuff, even if it was a copy, just for the pattern!
The Finns have also come up with a pattern to wear when there's a dusting of snow in the area of operations, but not enough to warrant the full white & gray suit. Again, this looks to be quite an effective pattern for its intended environment.
Then there's the classic German "Schneetarn" white & green/reversible to all white snow camouflage uniform. I've actually got a set of these on the way!
In my research of snow camouflage, I also found that the Russians have come up with another pattern for use in the snow. It's very similar to the German pattern, but the blobs are smaller. I don't have much information on it, though.
If anyone else knows any other patterns, or even has their own to share, please add them to the discussion! I know they're out there!