If you are looking for glass tiles, tumbled glass or some other mosaic material, mosey on over to Bedrock Industries. They are under the east end of the Magnolia Bridge where Elliott turns into 15th. They have a big yard full of miscellaneous materials, made of glass, stone, rocks and cement.
Someone put together a big list of mosaic links over at metafilter.com, and a commenter found some pictures on flickr.com of mosaics around Seattle sidewalks.
Zetamari is a website run by Angie from Seattle. She has a great eye for color and makes mosaic mirrors with a lot of flair. Check out the website for the gallery or mirrors, artwork and luxury birdhouses!
Mosaic Tile Arts is a mosaic tile supplier near Seattle (Hoquiam). I’ll be listing other suppliers in the area and other things of mosaic tile interests.