via Mylenium (and forums) is Claudio Miranda's real world lens flare tests, with some newer ones added. There's a lot going on beyond the basics with lighting, camera filters and lenses, etc. that lens flares can become obsessions to avoid, create, and recreate with shaders and filters like Knoll Light Factory.
Mostly tangential, check out "Father of the Lens Flare" podcast with John Knoll, "inventor of the digital lens flare, co-creator of Photoshop, 22-year Industrial Light Magic veteran, and modo user."
Update: via Prolost, see the SIGGRAPH 2011 paper, Physically-Based Real-Time Lens Flare Rendering; here's the video,
Physically-Based Real-Time Lens Flare Rendering (SIGGRAPH 2011 Paper) from Matthias Hullin on Vimeo.