I got married on Dec 7th. I am in US on L1 visa. Can I file taxes for year 2008 as married? As of today (20-Jan-2009) I have not received her social security.

You should be able to file married for 2008.

Yes if you are resident, you can file joint return as residents. This is true even if your spouse has never been to the U.S. and is non-resident. Attach W7 (ITIN application) with the tax return.

Hold on the Form W-7 application!

If you have submitted for a SSN for your wife, she is NOT eligible for an ITIN. You need to wait for the SSN.