The Cartography Lab's data repository is on "atlas" . Some of this is just ASCII data files and works ok for download via saving the file from your browser. SOme of it is more complex and not working right as of 10 Nov 1997.
The Geography 387 html experiments.
Jeremy Crampton's cartographic references are here .
ESRI has some impressive interactive mapping demonstrations as well as a bunch of useful resources on their web site.
There is a Java Mapping applet at GeoInfoSolutions. (This works if you have java installed.)
MAPSHEETS easy to use mapping and geographic data presentation software for Microsoft Office.
The tiff specification is available on the net. A good start is the unofficial tiff page. There is a pointer to the GeoTIFF site there also. Source code for reading/writing tiff files can be ftp'ed from here. This will compile under Win32. The original tiff specification can be found at Adobe.
Woolleysoft These folks sell software for terrain visualization. The can output VRML and have claimed on the net to have solved the problem of reducing geographic data volumes to levels manageable by existing browsers. Take a look and see whether you agree. Note the coarse appearance of the land cover data, and it's apparent mis-registration (I think that the dark patches are lakes, not burn scars.) This also took a few minutes to load on my PC. No, they have not solved all of the problems yet.
See also the Geog 488 urls.