Duranta? Up to 25 ft. but easily kept below 20 ft. I particularly like the variegated variety.

Ryan

I like my Chinese Fringe tree best out of all of my trees. Mine is still growing in a vase shape, although I see they do get wide as they age. Monrovia says they need weekly water. I don't know how much mine gets, since it lives on the overspray from a flower bed. 20-25 feet.
Renee

Here is a link that might be useful: Chionanthus Retusus

Check out Robinsonella cordata, with gorgeous blue hibiscus-like flowers. I just picked one up at the UC Berkeley Botanic Garden fall sale, and am anticipating the first time I get to see it bloom. I am also enjoying the fall blooms on my Cunnonia capensis tree in my front garden, but this is another rarer tree species that takes some searching to find. The Chinese Fringe tree is also quite nice or how about Cornus capitata?.

Another vote for chionanthus retusus here. I love mine. On the other hand, I just looked up David's Robinsonella cordata -- absolutely gorgeous! Winter hardiness rated at 25-30 degrees, which may be a problem in some inland southern California areas.

Kay

Thanks for those suggestions! I appreciate it.