Garritan is a software company that produces software that lets you create virtual symphonies. This is used by people who are composing music, either to commit to CD or to spec an orchestra piece before paying a real symphony to perform their piece. If you've been to a place like Bed, Bath and Beyond or Target, if you've seen those "Solitudes" CDs where it's like music with wave sounds, the orchestra accompaniment on those CDs are probably done using Garritan software. As a way to promote itself, give back, and give people a chance to play around with their software, they put out a CD each year of Christmas music. It's nearly always purely instrumental, public domain music, but there are still new arrangements and the music is beautiful. I discovered it a few years ago and hurry to their website each season to grab the new songs to add to iTunes.
You can find this year's collection here. There's a link there for the album art, a link to download the entire collection as a ZIP file, and links to their past albums as well.