Sometimes it's hard to find a good educational website that gives you the comfortable feeling that you can just let your students explore, knowing that they're bound to learn something in the process.  Voila!  I have the perfect spot for you--Lincoln Park Zoo, Z.E.B.R.A Online.  Start with the Students' Home Room where students in grades 3-5 have a variety of options, all of them dealing with animals in some way.  But wait!  This isn't your usual encyclopedic information source.  This one deals with adaptations, ecosystems, and generally shows the ways that we are interconnected with all of nature.  Students can play games that aren't just edutainment, listen to interviews with zoo experts, and check out the animal stories that make students read, think, and make choices.  Everything is interactive and engaging.  I also visited their list of links to other sites—all informative and safe.  Take a look at this great website and make a note to use it in your upcoming lesson plans!