I've created a fancy phylogenetic tree of life on Earth. It's split up roughly by class:
I'm afraid it won't work for every browser. If it shows up at all you're probably good to go, but if there are problems, you can always look at the ASCII files instead.
It's pretty interactive: click on the underlined leaf nodes to expand sub-branches, and click on the silly little boxes that appear to collapse them again. At first it just displays stuff that I considered "important" (this is obviously extremely subjective!) There is a "link" below the tree that will show the full tree with thousands of obscure little dead-end branches that only a small handful of people in the world will ever see or care about.
Each page contains notes about the source or sources I used to compile each tree. In one or two cases I could write scripts to convert datasets downloaded from the web so I can guarantee a certain amount of accuracy... however most pages were stitched together by hand from multiple sources. I keep correcting mistakes I find, but I'm not likely to run out of them any time soon.
Modern phylogenetic trees contain far more than mere taxonomy; they show evolutionary relationships. The trees I've presented here are monophyletic, meaning that all members of a given branch share a single common ancestor not shared by any other branch. Old classification systems frequently grouped species by various obvious morphological features (such as details of flower parts). However these features often turn out to have evolved multiple times in separate lineages (like salt-tolerance in mangroves). Tremendous research has been done to identify better characteristics (such as mitochondrial DNA and odd enzymes) that provide a more reliable measure of evolutionary affinity. The field of systematics has really taken off in the last few decades. A virtual flood of genetic and molecular data has turned many of the old classification systems on their heads. Things are still in rapid flux, but I think we are starting to get a pretty good idea what the final product will look like.
The depth of the trees vary greatly. As a general rule depth (absolute depth, at any rate) is fairly meaningless in phylogenetic trees. What one botanist calls a family (such as the pine family, Pinaceae) another might elevate to an order (Pinales). However the following table of endings should help you keep track of the rough level in my trees.