Some links for sites on Willem de Kooning

Museum pages:

Guggenheim Museum
The Guggenheim museum, N.Y.
Museum of Modern Art
The Museum of Modern Art, N.Y. 1997 Exhibition of De Kooning's late work.
National Gallery of Art
The National Gallery of Art, Washington, D.C.
Hirshhorn Museum
The Hirshhorn Museum and Sculpture Garden, Washington, D.C. Look for De Kooning on their site. It's the world's largest museum collection of De Kooning's work.
Artseensoho
Artseensoho, N.Y. Drawings on paper and vellum.

Gallery pages: see the various links in the list of published works.

Other pages:

Artnet
A service page on behalf of galleries. It offers images as well as information about more than fourty works by De Kooning, that are for sale.
Askart
Various information and images for free, otherwise for members.
Artchive
Mark Harden's art site.
Sally Yard
Sample pages from Sally Yard's book on De Kooning.