The Lodi Visitor Center is a great resource. Zinfandel is king in Lodi, but there is definitely alot of diversity in terms of wine style and type of wineries. Klinker Brick, Cycles Gladiator, and Jessie's Grove are all must visits.
Not to knock anyone down, but i would pass on Delicato and Mondavi. They can be good resources for getting to know wine and getting to know the Lodi appellation, but if you ask honest questions you are bound to get some passionate wine geeks (or even a winemaker) who will be happy to talk your ear off.