Volcano World claims to be the web's premier resource site on volcanoes; includes an updated list of current volcano eruptions; written for student readers, http://volcano.und.nodak.edu/
More about volcanoes at Michigan Technological University's volcanoes page, http://www.geo.mtu.edu/volcanoes/
Nasa has an Earth Sciences site, with education resources and a kids section at http://www.earth.nasa.gov/
The US Geological Survey encyclopedic site is at http://www.usgs.gov/
To see virtually any mineral you could name, including enlargeable thumbnail pictures, try the comprehensive listing of minerals at http://mineral.galleries.com/Minerals/By_Name.htm
Cloud pictures with clear descriptions can be viewed at http://vortex.plymouth.edu/clouds.html
Lots more about clouds at this site which links to information resources (including pictures) and instructional materials http://www.cln.org/themes/clouds.html
Watch this space for more great geology links