CGSociety Feature Tutorial Environment Concept Art: Composition – Philip Straub
Good tutorial on basic rules of composition.

The Colorscript
A quick look at colour scripts and how useful they are as a pre-production/previs tool.

Color Theory for Cinematographers
A look at a colour theory for cinematographers with a film mosaic at the end.

Cinema Redux
A nice piece of software for grabbing frames from movies at regular intervals to look at the colour script.

Light & Shadow
Words of wisdom from master cinematographers

Visions of Light (1992)
Cameramen and women discuss the craft and art of cinematography

“The Cinematography of “The Incredibles”
A look at the cinematography of the Pixar movie

DSLR Fimmaking –
Very good video tutorials covering pretty much everything you need to know as a beginner to DLSR Flimmaking.

Philip Bloom’s DSLR video tutorials on Vimeo

VFX of The Hobbit: The Desolation of Smaug – Virtual Cinematography

Key Texts:

CG Cinematography by Chris Brejon

Painting with Light – John Alton (Author)
Publisher: University of California Press (9 May 1995)
ISBN-10: 0520089499
ISBN-13: 978-0520089495

Light for Visual Artists: Understanding & Using Light in Art & Design – Richard Yot (Author)
Publisher: Laurence King; Reprint edition (25 April 2011)
ISBN-10: 185669660X
ISBN-13: 978-1856696609

If It’s Purple, Someone’s Gonna Die: The Power of Color in Visual Storytelling – Patti Bellantoni (Author)
Publisher: Focal Press; 1st American Pbk. Ed edition (12 July 2005)
ISBN-10: 0240806883
ISBN-13: 978-0240806884

Sight, Sound, Motion: Applied Media Aesthetics
Herbert Zettl (Author)
Publisher: Wadsworth Publishing Co Inc; International ed of 7th revised ed edition (31 Jan 2013)
ISBN-10: 1285081234
ISBN-13: 978-1285081236

The Five C’s of Cinematography: Motion Picture Filming Techniques: Motion Pictures Filming Techniques – Joseph V. Mascelli (Author)
Publisher: Silman-James Press,U.S.; 1st Silman-James Press Ed edition (1 Oct 1998)
ISBN-10: 187950541X
ISBN-13: 978-1879505414

Film Directing Shot by Shot: Visualizing from Concept to Screen (Michael Wiese Productions)
Steve Katz (Author)
Publisher: Focal Press / Michael Wiese; 1st ed edition (1 July 1991)
ISBN-10: 0941188108
ISBN-13: 978-0941188104

Film Directing: Cinematic Motion: A Workshop for Staging Scenes
Steven D. Katz (Author)
Publisher: Michael Wiese Productions; 2nd Revised edition edition (14 May 2004)
ISBN-10: 0941188906
ISBN-13: 978-0941188906

Must watch documentaries (in alphabetical order):
Cinematographer Style
Colour: The Spectrum of Science ​
Everything is a Remix
Light and Dark
Light & Shadow
The Code
Visions of Light

Must watch movies (in alphabetical order):

2001: A Space Odyssey (1968)
Apocalypse Now (1979)
Baraka (1992)
Blade Runner (1982)
Black Hawk Down (2001)
Braveheart (1995)
Citizen Kane (1941)
Collateral (2004)
Crouching Tiger, Hidden Dragon (2000)
Dreams (1990)
Drive (I) (2011)
Eternal Sunshine of the Spotless Mind (2004)
Fight Club (1999)
Finding Neverland (2004)
Gangs of New York (2002)
Gladiator (2000)
Hero (2002)
Home (I) (2009)
In the Mood for Love (2000)
Inception (2010)
Koyaanisqatsi (1982)
La Haine (1995)
Lawrence of Arabia (1962)
Legends of the Fall (1994)
Lock, Stock and Two Smoking Barrels (1998)
Lost in Translation (2003)
Once Upon a Time in the West (1968)
Raging Bull (1980)
RocknRolla (2008)
Run Lola Run (1998)
Saving Private Ryan (1998)
Seven Samurai (1954)
Seven Years in Tibet (1997)
Sherlock (2010– ) – BBC TV Series
Sicario (2015)
Taxi Driver (1976)
The Aviator (2004)
The Godfather (1972)
The Grand Budapest Hotel (2014)
The Last of the Mohicans (1992)
The Life Aquatic with Steve Zissou (2004)
The Shawshank Redemption (1994)
The Silence of the Lambs (1991)
There Will Be Blood (2007)
Wallace & Gromit: The Curse of the Were-Rabbit (2005)

See the list of Academy Award for Cinematography winners and contenders here

Online forums/resources:
The American Society of Cinematographers