I agree with Wchane on opting for Vietnamese or Mexican.
I really like Saigon 75 one block from San Jose City Hall. It's more upscale than the mom-and-pop places farther from downtown (assuming you're staying at one of the hotels downtown).
Here are some other options from my site...
If you're coming all the way from the east coast I'm suggesting you grab mexican or vietnamese.
i'm not too sure about the best tasting mexican, usually the hole in the walls do it for me - la taquria, etc.
However on vietnamese I like Tamerine in Palo Alto, or there are a variety of cafe/bistro style joints in s.san jose. Google for Broken Rice.
If you have access to wheels, you can also consider:
Alexander's Steakhouse in Cupertino
Restaurant James Randall in Los Gatos (I think they still have prix fixe during the week)
10330 N. Wolfe Road, Cupertino, CA 95014
James Randall Restaurant
303 N Santa Cruz Ave, Los Gatos, CA 95030