I've just been made aware of CultureHall and I think you should have a look.
From the site:
Culturehall is a curated online resource for contemporary art where selected artists can share their work with curators, gallerists, collectors and other artists. We provide free artist portfolios with an easy to use set of web-based tools to make presenting art online simple and efficient. Our community of artists consists primarily of MFA graduates, arts professionals and teaching artists. Membership is available by invitation or application.
The site is run by David Andrew Frey and Tema Stauffer