Green Flash - Several pictures of green flashes, with an explanation of why it occurs. - http://www.weatherscapes.com/album.php?cat=optics&subcat=green_flash
Galax Lux Green Flash Gallery - Contains mostly green flash pictures, with some others thrown in for fun. - http://www.intersoft.it/galaxlux/GreenFlashGallery.htm
An Introduction to Green Flashes - Phenomena seen at sunrise and sunset when some part suddenly changes color from red or orange to green or blue. - http://mintaka.sdsu.edu/GF/
Wikipedia: Green Flash - Explains what they are, and when to see them. - http://en.wikipedia.org/wiki/Green_flash