Here are some links to (mostly) local suppliers of landscaping products. They are a good place to visit (both online and in person) if you're looking for samples, ideas, or a place to buy.
STONE AND PAVING
Paving Stone Supply (a wide variety of paving to look at, Ballard)
Mutual Materials (brick, rock, pavers, etc, a big local company with various locations)
Lakeview Stone & Garden (a nice small rock yard you can visit in town, downtown Seattle and University Village)
Marenakos (North Bend, the major rock place, big stuff, small stuff, all rock all the time)
Rock Mountain (Redmond, smaller and not as well known as Marenakos but friendly, knowledgeable, and closer)
Abbotsford Paving Products (manufacturer of pavers and stack stone, Vancouver B.C. but available at Paving Stone Supply above)
SOIL, MULCH, SAND, GRAVEL
Pacific Topsoils, Inc. (various locations, drop stuff off, pick stuff up, soil, mulch, gravel, sand, etc.)
WOOD
Dunn Lumber (various locations, forget big box lumber - go local for better quality and service)
POTTERY
AW Pottery (Lynnwood - wholesale only, but we can get it for you)
SEED COMPANIES (all out of state, online ordering)
TOOLS
Scythe Supply (custom sized European scythes, the green way to cut grass, also mow small brush like a string trimmer never could, look cool, scare small children, based in Maine)
Hida Tool (in Berkeley, CA but excellent source of Japanese tools, online shopping)
Sunbelt Rentals (various locations, what's in their juice? these guys have always been friendly and helpful)
Aurora Rents (rentals, Shoreline and Greenlake area)
CONCRETE
Salmon Bay (Ballard)
Cadman (Redmond, other)
MISCELLANEOUS
Seattle Fabrics (outdoor fabrics and related hardware, Greenlake)
IMEX (King County's Industrial Exchange site, sometimes great stuff, sometimes free!, you never know)