Cladogram, tree of life, cladistics, taxonomy in JS or canvas?

I've been researching this same question myself for nearly a year now. The best library that I've found to date is d3.js, the successor to protovis.js. The good news is that the d3.js dendrogram and node-link tree should be sufficiently flexible for any/all of your needs; but the bad news is that you're probably going to have to write your own taxonomy logic and interactivity logic.

http://mbostock.github.com/d3/ex/cluster.html

http://mbostock.github.com/d3/ex/tree.html

To address herby, the d3.js libraries do, in fact, use HTML5's inline SVG.
Abigail

ps: Found a tutorial on using the dendrogram interactive and how to build the taxonomy logic. http://blog.pixelingene.com/2011/07/building-a-tree-diagram-in-d3-js/