I collated this set of links while working with SUMaC during the northern summer 2007. I expect they will get out of date very quickly but at the time I collected this list it seemed better than any other similar compilation on the internet. I have checked them as of the updating of my webpage, November 2008.
Wikipedia on hyperbolic geometry
Pages with lots of links:
Interactive Java applets
From the geometry center
From "Geometry and the Imagination"
Hyperbolic tessellations by Sascha Rogmann:
From M.C. Escher
Jeff Weeks software
Random other links