The Geometry Junkyard and Geometry in Action by David Eppstein.
Wallpaper Groups and Hyperbolic Tessellations by David E. Joyce.
Center for Geometry, Analysis, Numerics and Graphics at UMass.
Geometry and Topology Address Book.
The Topology Atlas at York University.
British Topology Home Page.
Links to low-dimensional topology maintained by Mark Brittenham.
The electronic journal Geometry and Topology.