This is a link to San Diego Zoo where you can view live video feeds of animals in their enclosures, including elephants and pandas.
http://ictmagic.wikispaces.com/Science
Zoo U is an online game-based social skills assessment program for children in grades 3 and 4. After customizing their avatar, players explore a variety of social situations in a virtual school setting.
"In their new book, Debra Kidd and Hywel Roberts firmly place teachers, and ultimately their students, in a range of different locations, where the learning inhabits, offering a fantastically imagined context with prompts, ideas and illustrations helping exploration and discovery. In a fascinating resource book, which can be used in many subject areas, across most stages in schools, the authors break down each chapter destination (including a forest, castle, graveyard, ship, zoo, cave, theme park) into a story starter - introducing the location and providing provocative initial questions; key landmarks (either for primary or secondary aged students), a stopover - providing a more in-depth account of their learning journey; stepping stones - context based tasks provided to also prod your imagination, and; the bedrock - offering a debrief of the processes, helping teachers understand the justification of the processes undertaken."
A large collection of links to virtual "field trips". Not sure they all technically fall under the "field trip" classification, but it is a good collection of sites nonetheless. Covers all subject areas, but here are some examples for science: biomes, biomes of North America, clouds, constellations, Mars, microbe zoo, and many more.