If you haven't made it already I'd buy pit run and plant things enjoying or even demanding excessive drainage, like succulents, manzanitas, eucalypts, maybe an olive tree...Berm of very droughty looking soil adjoining parking area at Jungle Fever Exotics nursery, near Point Defiance Park has some examples of the kind of thing I have in mind.

A friend who lives in your vicinity had 88 species of cacti growing in his front yard at one time.

GardenWeb contributor I. Barclay has started offering rare plants of harmonious aspect on his Desert Northwest web site; see also his Ian's Plants Pages for photos of dryland/exotic plants here and elsewhere.

Perhaps the most gardenesque wild plant sites here in the Puget Lowland are balds, that is bedrock outcroppings where trees are excluded by thin soil. Here one finds sun-loving native bulbs (camas, onions and fritillaries), shrubs (including manzantias) and grasses that cannot survive in the nearby forest. A pit run berm planted with perhaps some of these as well as visually and culturally compatible, sun-loving, drought tolerant plants from other regions would depart from Bark and Junipers but still be quite in character with the region.

Here is a link that might be useful: Article - Trees that merit planting in Seattle by Arthur Lee Jacobson

Thanks for the suggestion bboy, I'll drive down to Jungle Fever Exotics and check the plants. I would like this planting to serve as a privacy screen as well. So I'd like tall plantings in most of the bed. I grew up in the SW desert, so cacti are not something I find very appealing, now that I'm living in such a gardener's paradise. But I'm sure the cacti that I could grow here are not the same as what I'm familiar with in the SW.

Other good places to look for "different" trees and shrubs are Bellevue Botanical Garden, Carl English Botanical Garden, and Washington Park Arboretum.

Here is a link that might be useful: Trees of Seattle