Heat-Line
Eliminate water lines and pipe freezing with Heatline frozen water pipe protection. Energy efficient internal & external water line applications and cable heat trace systems.
http://www.heatline.com/index.htm

Thermon Manufacturing Company
Thermon's specialty is "heat tracing"; the application of steam, fluid or electric heat to piping, tanks, instrumentation and other equipment.
http://www.thermon.com/

Bright Dyes Dye Tracing Products
Bright Dyes - Easy to see and easy to use EPA and NSF certified tracing dyes. TRACER DYE, WATER TRACING DYE, DYE TRACING, DYE, DYE TRACERS, TRACING DYE, TRACING DYES, LEAK DETECTION DYE, SEPTIC DYE, SEWER DYE, TOILET LEAK.
http://www.brightdyes.com

Global Trace Heating Ltd
Global Trace Heating Ltd manufacturers of quality trace and surface heating equipment for frost protection process heating of tanks pipes vessels and many special or one off applications
http://www.globaltrace.co.uk

Vidac Solutions
Integrator of process control, data acquisition and electric heat tracing systems.
http://www.vidacsolutions.com

Promac Inc
Promac: Industrial Process and Commercial Construction
http://www.promacinc.com

Nextron Corporation
An electronic manufacturer of industrial products that relate to monitoring and control of electrical heat tracing in process plants.
http://nextron.ca/

Ray tracing in Wikipedia
A overview non technical article on ray tracing also covering some history of the subject.
http://en.wikipedia.org/wiki/Ray_tracing

Ray Tracing News Guide
Lots of information on ray tracing. Updated once or twice a year.
http://www.acm.org/tog/resources/RTNews/html/

Ray Tracing News
An infrequent newsletter on ray tracing and general computer-graphics research and resources.
http://www.acm.org/tog/resources/RTNews/html/