For Arts Sake is one of my newest stockists. I absolutely love their website for their huge selection of contemporary art prints, and their love of Linocut. If you're looking to splash out, my absolute favourite pick is The Catch, bottom left, by Colin Moore. You may also like the work of Gail Brodholt who captures the essence of the London Underground beautifully in her work.
For smaller gifts and stocking fillers, fill your boots with chocolates from Coco Chocolatier, write cards from Canns Down Press and Cambridge Imprint, and gift matchboxes they'll want to keep and re-fill from Archivist.