Here is the largest pack of winter and Christmas backgrounds on Graphicriver which includes flares, glares, particles, lights, snowflakes, stars, bokeh, blur, and snow elements. You can combine multiple patterns so that you will get even more backgrounds. All patterns are the same size (500×500 72DPI).
How to use it? (the simplest way)Open the Preset Manager in Photoshop (Edit > Presets > Preset Manager) and click Load button, then browse to the .pat file and double-click it.
If you use old versions of Photoshop (released before 2009), place the .pat files into: C:\Program Files\Adobe\Adobe Photoshop x\Presets\Patterns (for Win)
~/Library/Application Support/Adobe/Adobe Photoshop x/Presets/Patterns (for Mac)
where x is the version number of Photoshop.