Theory & documents

Work of Breathing

The True Work of Breathing in Rebreathers (pdf, Jack Kellon)
Comprehensive Performance Limits for Divers Underwater Breathing Gear: Consequences of Adopting Diver-Focused limits  (pdf, NEDU, Dan Warkander)
Development of Comprehensive Performance Standards for Underwater Breathing Apparatus (pdf, Dan Warkander, Claes Lundgren)

Standards:

EN 14143:2003 (pdf)
prEN 14143:2010 (pdf)
EN 14143:2013 (link to webshop, cost of document is 18€)
NORSOK U-101 (pdf)

Oxygen sensors:

Oxygen sensors and their use within Rebreathers (pdf, Kevin Gurr)
Oxygen Sensor Guide (pdf, Analytical Industries Inc.)
Understanding_oxygen_sensors (pdf, Paul Raymaekers)
Oxygen sensors in rebreather applications - Guidelines for use (pdf, Analox)

Oxygen delivery:

Understanding_Constant_Mass_Flow.pdf (pdf, Paul Raymaekers)
Choked Flow of Gases (pdf, O'Keefe Controls Co.)

Patents:

Display integrated vibrating alarm (Kevin Juergensen)
Inspiration Vision & Inspiration Classic (Martin Parker)
Scrubber heat exhanger (Martin Parker)
A mouthpiece valve for closed-loop self-contained breathing apparatus (BOV) (Martin Parker)
Temperature-based estimation of remaining absorptive capacity of a gas absorber (Dan Warkander)
Variable volume ratio compound counterlung (John P. Kellon)
Soda lime half life indicator
Breathing apparatus mouthpiece (William C. Stone)

Scrubber:

The duration of two carbon dioxide absorbents in a closed-circuit rebreather diving system (Harvey D, Pollock NW, Gant N, Hart J, Mesley P, Mitchell SJ)
The CO2 Scrubber in a Diver’s Rebreather: how long does it work and how long does it actually last? 
Diving a Rebreather in Frigid Water: Canister Concerns (John Clarke's Blog)
A Look Inside Rebreather Scrubber Canisters, Part 1 (John Clarke's Blog)
A Look Inside Rebreather Scrubber Canisters, Part 2 (John Clarke's Blog)
DiveGear Express: O2ptima Scrubber Duration Test Results  
CFD Modeling of Breakthrough in Closed Circuit Rebreather Scrubbers (Cunningham S., Burke A., Kelly G.)
Carbon Dioxide Absorption and Channelling in Closed Circuit Rebreathers. (Dr. Shona Cunningham. Summary. Whole document?)

Misc:

A learner's guide to Rebreathers (pdf, Richard Pyle)
Biological Effect of Noble Gases (pdf, J. RŮŽIČKA, J. BENEŠ, L. BOLEK, V. MARKVARTOVÁ)
CEJN style Offboard Gas Supply Quick-Disconnect subsytem for CCR (pdf, Michael Lombardi)
Proceedings of Rebreather Forum 2.0 (pdf, 24MB!)
Rebreather Forum 3 Proceedings 
Proceedings, Joint International Scientific Diving Symposium, AAUS & ESDP, Curaçao 2013
Doomed To Repeat The Past? The Re-Circulating Story of Sport Rebreather Safety - Part 1 (pdf, Haynes Marine Ltd.)
Doomed To Repeat The Past? The Re-Circulating Story of Sport Rebreather Safety - Part 2 (pdf, Haynes Marine Ltd.)
A Survival Guide To Rebreather Diving (pdf, Haynes Marine Ltd.)
Safety Evaluation: Lithium Manganese Dioxide Batteries in a Diving Life Support Recirculator (pdf)
Fault Tree Handbook NASA (pdf)

Links:

www.rubicon-foundation.org (large collection of studies and articles)

www.phr.net.pl/ (research papers in polish and english)
www.rf30.org/ (Rebreather Forum 3.0 presentations and documents, NOT WORKING!)
www2.dan.org/research/conference/2008TechnicalDiving/Rebreather_Workshop.aspx (DAN 2008 Technical Diving Conference, Rebreather Workshop)
Youtube playlist of Rebreather Forum 3 videos provided by DAN 
South Pacific Underwater Medicine Society Public Journals (inc. rebreather and deco articles)