December is a pretty quiet month for the Con circuit. It seems that most people, aside from spending time with family and friends, are gearing up for the January cons/the 2011 con year in general.
Now, if you have the funds for it, is a good time to start planning your circuit and pre-registering. Prices are pretty low this early on for most cons starting in March.
The major cons, such as SDCC, will have pretty much sold out by now or have prices at their max, such as Anime Los Angeles.
As a quick note, as of today SDCC registration was closed due to "issues with registration." Hopefully this means there are still some tickets left for attendance and you'll have another chance to register. Also, their volunteer registration will open in January 2011.
Last note, SGIS con registration will open soon. This year's theme "Tea Party". Bring your best tea party/Wonderland outfit to the snow.