+1 on Iron Horse Trail for casual riding (sometimes I don't stop on it). Just be sure to call out if you're going to pass joggers/slow people/strollers or any combination.

Danville Blvd makes for awesome pacelining... Then you hit downtown Danville where you encounter the usual slew of things that make cycling complicated. Stopsigns, Starbucks and SUVs. Plus on holidays when our police force has even less to do they stakeout the stopsigns. It's all pretty gravy after it switches to San Ramon Valley Blvd though, because you're on you way to Dublin which is a nice crossroads out to Livermore or Hayward.