Artshole - provides professional, emerging and student artists with a free platform to showcase and sell their artwork. They have a free listings section which provides a good source of exhibition and events material and artists can have their own portfolio.
They have extensive lists of art universities in the UK and galleries in London, as well as listings for artists using photography, web design, film and animation, illustration, fine art, graphic design, painting, fashion and product design.
Their free portfolio service requires you to send them material by e-mail so is not instant, like most of the others in the field but, that said, they attract a lot of people willing to place 10 examples of their work on the site.
They don’t take commission on sales and have a physical gallery in London for selected shows.