The web contains many sources of valuable information about scattering of light and atmospheric optics.

Here are some of my personal favourites:

Piotr Flatau operates several useful sites such as SCATTERLIB(scattering software), HALOLIB (atmospheric optics - halos and rainbows) and REFLIB (detailed information about refractive index values)

Thomas Wriedt's comprehensive site concentrates on Electromagnetic Scattering Programs, but also includes many useful links to papers, etc.

Les Cowley's site on Atmospheric optics contains many images of ice halos and the magnificent HaloSim program for simulation of halos.  There is also an excellent section on scattering from water droplets, including the Iris program (based on the same BHMIE algorithm for Mie scattering as MiePlot) for simulation of coronas, glories and fogbows.

Raymond L. Lee Jr. offers on-line extracts from the book "The Rainbow Bridge: Rainbows in Art, Myth and Science", plus links to scientific papers including the classic paper  “Mie theory, Airy theory, and the natural rainbow” published in 1998 in Applied Optics 37, pp. 1506-1519

AKM Atmospheric Phenomena offers a wide range of impressive images of rainbows, glories and much more ....

Ken Scott's Touching the light web site includes some stunning images of Brocken spectres.

Bernhard Michel offers a Java-based MieCalc program