Wikipedia is basically free knowledge for everyone, by everyone; it is an online encyclopedia that can be edited by anybody. For example, in the first paragraph of the entry on Tyrannosaurus rex, the article mentions that T. rex is poorly known and rare at only 20 specimens as of 2001. "Only?" I know there are listmembers, both professional and amateur, who would have something to say about that!
Further, there is Wikispecies, which is an attempt to catalogue every known species to have ever existed, for anybody to access. This is a big task, but there is so much knowledge on this list that it would seem much smaller.