Living and working around the SF Bay Area, my current favourite drives are:
1. Highway 1 - Breathtaking scenery of the coast, sweet winding roads, and the knowledge that your Si better not falter because its a LONG way down :)
2. The Presidio Hills - much good turns and scenery. Looks like the Forest Track out of the PS2 Gran Turismo game.
3. I280 - A common favorite, you couldn't ask for a better daily commute. Big open lanes, sweeping curves, great view.