Hundreds of paintings from the on-line gallery complete with descriptions, fact sheets, artists' biographies, and even monthly podcasts and other podcasts about key paintings. There is also a 'Learn about Art' page with links to videos about the paintings, and an art glossary.
Actually, the Tate is four museums: Tate Britain with its Turner Collection, Blake, the pre-Raphaelites, Gainsborough, Hogarth, the twentieth century collection; Tate Modern with Picasso, de Chirico, Matisse, Rothko, Braque; Tate Liverpool; Tate St Ives. The main site gives on-line access to thousands of artworks. You can browse by artist, category, style, subject, or gallery.
An eclectic collection ranging from Byzantine ivories to British silver work to Mogul Indian mechanical devices to Arts and Crafts to modern stage costumes. An architecture gallery and design. See the video on 20 reasons to visit the V&E (there are many more than just 20!).
Descriptions of the collections, interactive guides to the more than 400 galleries, and a timeline of art history. There is also a link to the site of The Cloisters, a building incorporating parts of various medieval religious buildings; it houses the Met's world famous collection of European medieval art. For lovers of gardens and flowers, there is a blog dedicated to the Cloister's medieval garden.
Here you can find descriptions and images of MoMa's collection of modern art: painting and sculpture of course, but also films and photography, architecture and design, media and performance art.
A description of the Artwork of the Day, video and multimedia presentations of masterpieces in the series 'A Closer Look', high resolution images of key pieces in the collection, and the collection itself!
This site is not as user-friendly as some of the other sites. For example, you cannot simply browse the collection to see what is there. You have to search for artists one at a time. But there are three virtual tours with images of highlights from the collection plus a recorded commentary of the paintings.