Two very good sites worth exploring: Artcylopedia and A Daily Dose of Architecture.
Artcyclopedia indexes the images and information on great art viewable on gallery webpages. Relevant information can be found in multiple ways, such as searching for an artist's name or browsing through movements. I am impressed by the sheer number of artists documents and the absence of dead links. For example, check out the entry for Derain, an important but less popularly known Fauvist painter.
John Hill's architecture blog, A Daily Dose of Architecture, is updated daily with stunning images of actual and imagined structures. Every post conveys John's knowledge of architecture and passion for buildings both impressive and whimsical. Architecture afficianados will also appreciate the many well-organized links.