I live in New Jersey but work in New York City. Which tax forms do I use to file for 2008?

You will report your NY city income to both the states.

If you are present in a state, then any income earned during this period, must be reported to the state.
To your resident state, you must report your worldwide income for the year.
Read: Your U.S. Tax Return: Working or Living in Two or More states (http://taxipay.blogspot.com/2008/06/working-in-two-or-more-states.html)

You need to complete New York's non-resident income tax form IT-203, and NJ's resident tax form NJ-1040. Also the federal 1040 of course.