JavaScript libraries to draw your own diagrams
Personally I've found dagre-d3 to be by far the best library when presenting actual useful graph data: https://github.com/cpettitt/dagre-d3.dagre is a layout library which implements graphviz in javascript, and renders it in d3.  d3's force-directed layout is great for demos, but I've never found it good enough when trying to represent real data.(edit: a link to my own simple, albeit demo, page using the library: http://nlpviz.bpodgursky.com/home)