Some of the area bike clubs have ride sheets on their websites. Here are the routes for the club to which I belong (Valley Spokesmen):
http://www.valleyspokesmen.org/routes.php
These are arranged by the starting area and are rated for hilliness (1 = flat, 5 = mountain) and distance.
It sounds like you like to ride some hills, so in addtion to Diablo I'd suggest Redwood, Pinehurst, and Skyline roads north of Castro Valley, Morgan Territory to the east of Diablo, Palomares Rd. south of Castro Valley, Calaveras, Felter, and Sierra south of Sunol, and Mt. Hamilton a little farther south.