Are there any? I didn't think so.

I think that's why there have been no responses yet. Flowering cherries are not an ideal choice for a woodland garden or much shade. In fact, in the PNW they develop considerable disease and insect problems even when planted in ideal conditions.

For an early season bloomer more suited to a woodland or shady garden I'd suggest Amelanchier (serviceberry), Cornus kousa (Korean dogwood), redbud (Cercis canadensis, or if you can find it, the better performer for our area, C. occidentalis or western redbud). If early blooming is not a requirement, I'd go with Stewartia pseudocamellia - probably the best all-season tree for a woodsy, understory planting area.

None of these are exactly what I'd consider very drought tolerant and the stewartia will definitely need supplemental irrigation in our dry summers.

Thanks for the great suggestions gardengal! The list will help me fill all those empty spots in my garden.