Hello, I got married last year Nov 2009 in India,
Both my wife and I reside/work in the US on H1B visa,
We did not notify our married status to our employers
So our 2009 W-2 says "Taxable Marital Status" is Single.
Are we still allowed to file taxes as Married Filing Jointly?
The only proof we have is the marriage certificate from
India, please advise, thank you.

Does your passport show your wife's name and your wife's passport show your name as husband? Did you register you marriage in India?
If you have marriage certificate from Registrar in India, yes you can file joint return.

If you are legally married, then you must file as married. I do suggest that you file a new W4 with your employer to update their records.

Thank you both for your replies, actually I just found out that
We don't have a marriage certificate yet, so the only proof we
Have is wedding photos of the Indian ceremony (which took
Place in Nov 2009), is it still OK to file as Married Filing Jointly?

If you in fact are legally married in India and are awaiting the marriage certificate, then file Married Filing Jointly.