I am in usa on L1a visa since July 20th 2008.
I am married and have kid. I am from India.

I have question about tax filing and residency status

I have less than 183 day in 2008 but I will stay in usa in 2009.

What will the best approach to file tax for me?

You can file resident tax return as Married Filing Jointly.
You will have to wait to file your tax return till you meet the Substantial Presence Test (of 183 days) in 2009.

You will get standard deduction of $10,900 and exemptions for both of you.

You must both declare your worldwide income for 2008. If you have any foreign income, and on that income you paid taxes in the foreign country, then you can claim foreign tax credit (Form 1116) or you can use Foreign Earned Income Exclusion (Form 2555).
Read about L1 tax filing: Your U.S. Tax Return: The U.S. Visas

Thanks MukatA.. So I have to file an extension.
Now the question is that I have to wait full 183 days in 2009 or there is any other calculation.

You complete SPT in 2009 in 183 days minus 1/3 of days in 2008. Read Your U.S. Tax Return: Substantial Presence Test

Thanks Again..

Is this called First Year Choice?

Because IRS says in a note that

"You do not have to be married to make this choice."

Publication 519 (2007), U.S. Tax Guide for Aliens

This is the Married Filing Jointly option under irst Year Choice, which DOES require that you be married.

First Year Choice by single persons allows the single person to file as a dual-status alien, not as a resident alien.

You are essentially making two elections -- first year choice to be treated as a resident and a joint return election so that you and your wife are treated as residents for the entire year.