The problem with gardening under pine trees is the need to constantly rake up and dispose of pine needles. So be prepared. My suggestions is to go native . . . ferns thrive in the shade and acidic soil. I've also had good luck with epemidium, snowberry and sweet woodruff. You can try knicknick, native ginger, etc., but in my experience they're harder to get established. Vine maples work well as smaller understory trees, and you can always go with Oregon grape, native ribies, etc. etc. For non-natives, Japanese maples and hostas do well in our shady acidic soil, as do azaleas and rhodies. Irises add a nice punch.

Regardless of what you decide to do you'll need a good broom for the paved area and a good lawn rake for the planted areas and a way to dispose of the never-ending pine needles. If you don't already have it, buy yourself a copy of the Sunset Western Garden Book -- it's the bible of gardening in the west. And have fun!