I would like to call attention to the Twin Peaks 50/50: http://www.twinpeakstrailmarathon.com/
It will be the inaugural race in February 4th, in beautiful Orange County. The race will take place on the "Saddleback", or Modjeska and Santiago Peaks. If you run the 50 miler you will have the chance to summit both peaks. AND you have a choice of which one to do first. (Santiago is higher, so it'll be interesting to find out what kind of strategies most people will use and which works best).
I know the race director personally and I see the effort she's putting into this race. She's getting big sponsors, and is really doing a great job organizing this. All proceeds will go to the Tucker Wildlife Sanctuary. What else can I say.... It's going to be a TOUGH course, great for those who love a challenge. The field is limited to 100 runners, as of now there's about a dozen signed up, but she would love to see a full field!
Just though I'd through it out there. If you are close to the Orange County area, you should consider this race. Oh, and it's cheap, too. At $50 and $60 for the 50K and 50M, respectively.