Blender Cycles Realistic Snowflakes
Here's the deal
In the scene, there are 7 flat planes, that can be animated though an emitter. If you import the particle emitter to your scene, you have instant snow. Looks great from a distance, and quality enough for closeup renders as well.
Each snowflake has a dimensional "high-Poly" version as well-- to be clear the high-poly versions are a series of places offset by random scale and rotation. On those planes is a textured material setup of a photo-real snowflake texture.
High poly and low poly can be used in the emitter, but I recommend using only the single plane, low poly versions of the snowflakes.