USGS page on the main types of plate boundaries

Source: USGS

Why Do Volcanoes Occur?

Earthquakes home at the US Geological Survey

Realtime earthquake data

Volcano World

Terrific activities from the Southern California Earthquake Center

Using space technology to observe and measure plate tectonic motion (try the Activities!)

For some real fun, download the iView3D freeware 3-D model viewer, and then go to the Scripps Institution of Oceanography Visualization Center and get the file called the "Engdahl catalog", which plots 77,000 earthquake events on a globe.  With the iView3D viewer, you can look at them from virtually any angle, and "see" underground!

The Virtual Silurian Reef

Plate Tectonics animations from the USGS

The Paleomap Project

From the University of California, Santa Barbara
 

NEIU "NASA/UNCF Project" module on Volcanoes

The USGS gives an activity similar to the one on 
this site, but more pre-packaged, with handout sheets and maps that you can print out, suitable for grades 4-8.

Just for fun:  Zoom out of Chicago  (Video courtesy of NASA/Goddard Space Flight Center)