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.