California buckeye (Aesculus californica). Deciduous shrub/tree. Wonderful bark, impressive flowers and decorative shiny round seed pods (called buckeyes or horse chestnuts) make this a good choice for larger gardens, especially with rock outcroppings where the roots can grow around and over the rocks as the plants mature.
Boxelder (Acer negundo) Deciduous tree. Riparian, prefers regular moisture as along stream banks. It’s not really grown for its flowers, but they’re quite ornamental, especially when backlit.
Western Redbud (Cercis occidentalis) Deciduous shrub/tree. Easy to grow, but not especially rapid. Prefers drier conditions.