Bell Atlantic maintains the Earthwatch resource, including photos, videos, data sheets, maps, and conferences. Treks have involved building solar ovens in Kenya, surveys of whale life, and areas where global warming can be observed. It has been piloted in New Jersey and the Washington DC area schools. Excursions change several times a year.
Space Weather, updated daily by Dr. Tony Phillips, looks at current events outside our atmosphere -- meteor showers, solar flares, auroras, and near-Earth asteroids -- providing dynamic, ever changing topics for research and exploration.
For younger students the Brookfield Zoo in Illinois draws in viewer participation by their becoming lost on the Ways of Knowing Trail. Researchers, rangers, local folks and the viewer must select the right choice points at various branches in order to find their home.
The British Museum is a trove of so many curios--artifacts from ancient civilizations--that the best way to navigate this site is to review the Web site once a year or so and select a topic to enhance your classroom. Included is Compass for Younger Students, presided over by Alfred the Lion.
This site lists hundreds web sites which students can use as stepping stones to research projects. Use Search to find a site that matches your needs.