Do i need ID if i travel to Tijuana(Mexico) from San Diego,Ca. for a couple days?What's entry requirements?

Yes, you need ID. Getting into Mexico might not be a problem without it, but in order to get back into the USA, you'll need a passport.

It is very clear that you need a U.S. Passport if you're going out of the country, even if it's just the border. Once you cross that border, you will need a Passport, otherwise you're stuck there. Take other ID's with you, such as a driver's liscence, or birth certificate, just in case.

You do not need a passport to enter Mexico by LAND until June of 2009! See website below and scrol down to the paragraph that begins with "June 1, 2009" in bold print.

As of right now you do not "need a passport" going by land or sea to Mexico. Eventually you will if they stay on track about passing that policy in 2008. The link below will tell you exactly what types of identification are acceptable.
http://travel.state.gov/travel/cis_pa_tw/cis/cis_970.html#requirements

What is your nationality?
" entry requirements in which country? In mexico you dont need anything, you just keep waking and there is Tj.
To come back to usa you need a driver lic to show it as your identification, If you dont have a passport, (usa) now if yo have a passport, bring it with you, If you loose all your identifications in mex. when you come back you ll tell it to the officer and no problem. Al long you say the truth, you wont have any problem. I suppose you are american or you have your papers, right? if you dont have papers, jump the wall

Drivers License only

a US Government issued ID is a MUST