Broad question. What do you like to do? What are your interests? Food? hiking? Beach? History? How much time do you have etc? Will you have a car?
High-level ideas are Portland, Seattle, San Francisco, LA and San Diego are the obvious starting points. If you have a car, then it opens it up to seeing places like Crater Lake in Oregon, catching theatre/ Shakespeare at the wonderful Ashland Oregon Shakespeare festival (some plays run through November), Mt Shasta and Mt Lassen in Northern California (if you like volcanoes and hiking), the rugged Mendocino coast and cute town (lots of artists and galleries), wine country of Sonoma (I prefer it to Napa). You may even catch the wine harvts/crush (http://www.heartofsonomavalley.com/products/2011-sonoma-valley-crush).
Be more specific about your interests, time and mobility to get more detailed advice and suggestions. Also, look up other California questions in this Q&A as there are lots of similar ideas for you to review. about 9 years ago