My community:
I donated blood twice this year and plasma (not the 4th state of matter) four times. (Same thing i've done ever since i turned 18).
At December 31st i'll short out all the spare change i've been placing in a jar during these last twelve months, and then donate the sum to my favourite charities (doctors without borders and two local ones, a child's smile and make a wish, for children with cancer).
This year in particular i tried to do a thing that overlaps my RL community and this wonderfull, on-line one, of which i am a proud to consider myself a member.
Unfortunately, it didn't go very well (as in number of responses that i thought i would get), but i learned the valuable lesson. Contact the mods and admins, and ESPECIALLY the person that originally came up with the challenge, BEFORE you post that you'll give money to anyone that makes it!
As for what i've done for the actual Orbiter community:
Not much, perhaps i've answered a couple of questions for newbies and i've placed one or two interesting posts in the tutorials and challenges forum.
Hope next year, i'll do better.
Have a GREAT New Year!