Decorator's Best - Designer wallpapers available by yard/roll online.
Paper My Walls - A great grasscloth source.
Hygge & West - Sells some of our favorites like Oh Joy! and Rifle Paper Co. They even have a removable wallpaper tile section!
Walnut Wallpaper - Great selection of unique designs.
eBay - You hate it or you love it, but every now and then you can find a great deal on a hand painted silk knock-off or out of stock Anthro papers.
Rebecca Atwood - Hand dyed and printed fabrics and wallpapers from a Brooklyn based designer.
Walls Need Love - The ultimate source for removable wallpaper.
Anthropologie - An expertly curated selection of wallpapers from all of the greats.