Hwy 128 going east towards Berryessa is awesome! Great for aggressive riding and just as lovely for relaxed touring.
Here's a good loop. Take 12 from Santa Rosa over to Napa, then hook a left on 29/128. Follow that north, stay on 29 (128 peels off to the right) and visit some of the wineries. (I recommend Castello de Amorosa halfway between St. Helena and Calistoga.) At Calistoga, take a right to stay on 29 and take that up to Middletown. Awesome twisties.
No gas stations after Middletown until you get back on 121 to Napa, so gas up in Middletown.
Just a mile or so after you've gone through Middletown, take another right on Butts Canyon Rd, which later turns into Pope Valley Rd./Chiles Pope Valley Rd. More awesome twisties.
Then it dumps you back into 128, take a left (east), back toward Lake Berryessa. More awesome twisties.
When you get to 121, take a right (south). That will take you to Napa and 29 - where you can catch 12 back to Santa Rosa.
That whole loop can take anywhere from 3 hours, to all day long, if you want to stop and enjoy all the sights.
I've done this ride a few times, I'm sure you'll enjoy it.
Just enter Santa Rosa CA on the google maps and you'll see the route clearly.
Enjoy my lovely state of California, and if you like wine, we have some of the best in the world!
Castello de Amorosa