My favorite dog-friendly hike spot is gorgeous right NOW. Sibley Volcanic Preserve, written up a year or two ago in the New York Times by Piedmont's Patty Brown, is in full bloom NOW. Great raptors and bluebirds, wildflowers, rocks (after all, as the material in the shelter points out, this is NOT the latest red hot chili pepper jelly, despite the name), relatively flat, some strollerable. Take Snake Road to the top, left just past Huckleberry Preserve.
My best walk: Up the first hill, left at the fork and through the cattle fence, continue about a mile around to the left (labyrinth if you go right at the second fork), heading for the hilltop with a patch of bay laurel (the knob with what looks like a single tree is a great lookout for kids). Veer right at the bathtub water-trough, check out Mount Diablo (and the snow-topped Sierra a couple of times each winter), and then head up to the stand of trees for a fabulous view of the Golden Gate. See if you can find the six labyrinths in the Park!