If you're regularly hiking Mt. Tam, I presume you're familiar with the double dipsea course, which would give you ~4500 ft vertical over 14 miles as an out and back from either stinson beach or mill valley. I agree with most of the east bay/south bay suggestions and would add Montara Mountain in Pacifica, which has awesome views. Check out Brazen Racing, Inside Trail Racing and Coastal Trail Runs for more ideas - they all organize Bay Area trail races and have course maps with elevation profiles posted online. For a very long day trip or a weekend I'd recommend Rocky Canyon trail to Pyramid Peak - the unmarked trailhead near Strawberry on Hwy 50 is hard to find, but it climbs 4000+ feet in <4 miles, so it's longer and steeper than anything in the Bay Area, as well as higher (9983ft summit).
