Update 18/10/2022: Gpvdm now has a ⭐new name⭐, it is now called OghmaNano. Please go to https://www.oghma-nano.com to get the latest version of the software and documentation.
It is hoped that this new name will be easier to say and remember. For a history of OghmaNano/gpvdm click here.
This is a rather useful database of n/k values. It's the biggest and most organized database I know of refractive index values. I try to sync gpvdm to it every couple of months or so refractiveindex.info It's maintained by Mikhail Polyanskiy.
PV light house run by Keith McIntosh, with contributions from many others.
If gpvdm does not fulfill your modeling needs, Juan Sanchez maintains a nice list of device modeling tools over at TCADcentral. He also publishes a nice looking 2D drift diffusion solver at www.devsim.org
Scientific photovoltaic software
Slivaco also do an Generic solar cell simulator, although it looks like it costs money.
The people at TU Delft also do a simulator which is pretty comparable to gpvdm in terms of featuers. I've not personaly used it though.