With its modified Mediterranean climate (cool dry summer and cool damp winter, instead of hot dry summer and warm rainy winter), Seattle has some great thyme lawns. Need full sun and good drainage. Weeding with a dinner fork may be required. Not necessarily a low-upkeep endeavor.

Creeping Taiwan raspberry or creeping jenny can carpet the ground nicely, when happy. The raspberry actually suggest shingles. Liking good moist soil, as do magnolias these would be more in character with these humid climate trees than thyme. All low creeping plants will have to be hand-weeded indefinitely, as they are not deep enough to exclude tree and shrub seedlings or other assertive weeds. Mowing is certainly less time-consuming.

The choice of groundcovers for this area is vast. I'd suggest visiting a good local garden center and investigating their selection. You're sure to turn up something great.

The Taiwan creeper (Rubus calcynoides) bboy mentions is one of my favorite groundcovers. A very tough, durable plant that will layer on top of itself to eventually develop an entirely weed-free barrier. Also evergreen and develops a nice bronze winter color.

Some thymes are quite tolerant of partially shaded conditions but can become a bit sparse compared to those growing in full sun. And a thyme lawn in bloom will attract just as many bees as clover :-) Another low growing but more shade tolerant choice is sandwort, Arenaria balearica.

What about a native: Knickanick?

Or rather than groundcovers, maybe a shrub border with different kinds of shrubs planted close together to crowd out weeds. Most groundcovers don't keep weeds out very well, especially the kinnickinnik. Some shrubs stay rather low and you could mix different heights and bloom seasons. So many possibilities here. Cruise around in nurseries and see what appeals.

I like salal, but it is slow to spread and establish, but once it's in it keeps weeds down pretty well and never needs watering because it's native. I also like viburnum davidii, it's an evergreen one that spreads more than it gets tall, will want either part shade or some water. It crowds out weeds very well. So do the various euonymus and they come in different leaf colors too. Rockroses like dry sun and bloom in spring.

You could grow Fragaria chiloensis. It is a nice lawn substitute - it doesn't totally block all weeds but it's as good as anything and spreads very quickly.

Personally I think something like Ceanothus prostratus would be really cool (especially on gravel) but you'll have a hard time finding a lot of those.