Links to some interesting websites:

American Masters - Billie Holiday

The Official Web Site of Billie Holiday, Index

The Unofficial BILLIE HOLIDAY Website

Billie Holiday - Artist Name's Official Website on Sony Music

Allmusic, which contains numerous informations on Billie Holiday's recordings

Billie Holiday - a Belgian Homepage with A LOT OF FINE PHOTOS!

Billie Holiday - Wikipedia, the free encyclopedia

Billie Holiday on YouTube
A lot of recordings of Billie Holiday with different fine - and not so fine - pictures

And finally a little gem:
Madeleine Peyroux - a young singer who is influenced by Billie Holiday but sings in her own personal way