It's of course, important to study real elements when creating them digitally. That is very true with fire. The more you study it the more you realize the wide variations of fire and the many forms it can come in. For your convenience and mine here are some good links.
http://celestiniosity.com/wp-content/fire.jpg
http://www.sces.uk.com/content_images/flame1.jpg
http://en.wikipedia.org/wiki/Fire_photography
http://my.firereference.com/
http://www.firephotography.com/
http://www.firegroundaction.com/
http://www.shutterfly.com/progal
http://www.printroom.com
http://www.pbase.com/fotoguy77/mikes
http://www.juanguerra.smugmug.com
and a awesome rocket launch reference
http://www.wghartenstein.com