Once again I am afraid my own interests will come to the fore here. I know nothing about contemporary music or the cinema - you will have to find those sites for yourself!
Language and literature
Libraryspot - has wonderful links to so many interesting sites.  I have mentioned it elsewhere - it is one of the really good resource links.
The Literary Companion - a delightful site to browse.
The British Library - full of treasures; have a look at the Gutenberg Bible
Biography Resources - the largest guide to biography sites on the Web.
Poetry Archives - lots of poetry resources; search by author or first line.
Fine arts
Mark Harden's Artchive - wonderful reproductions of hundreds of beloved works of art.
The Hermitage - take a tour of the treasures in St Petersburg
Classical music
British Orchestras - a good site with lots of links to other classical music sites
Classical Net - repertoire, recommendations,, reviews and links, with a search engine and composer Index.
Lovely things to look at
Flower Scans - the site owner scanned these flowers from life - placing the flower on the scanner, not an image of the flower. Admire their clarity and beauty.
Big Blue - just for sheer pleasure, explore this lovely, interesting and well-designed site.