Where can I get on-line information on active and erupting volcanoes?

You can find what you're looking for in Volcano World in Update on Current Volcanic Activity. You can also look under Other Sources of Volcanoes Information. Included in this section are links to the Smithsonian's Global Volcanism Network which has and excellent summary of every erupting volcano in the world. You will also find links to the volcano observatories in the United States (Alaskan Volcano Observatory, USGS Hawaiian Volcano Observatory, USGS Cascade Volcano Observatory, and around the world.