+1 for d3.js and the sentiment. After about a year of using highcharts, for a specific custom chart project, I was given the opportunity to learn and implement

+1 for d3.js and the sentiment. After about a year of using highcharts, for a specific custom chart project, I was given the opportunity to learn and implement it in d3. I built my first line chart by hand which took me little more than a week and then the custom chart project in about two weeks. It was definitely the most exciting project I have worked on so far. Learning d3.js also made me rethink my 'use javascript as necessary' policy. I also came to appreciate what other charts libraries like highcharts do, but I won't be using those other libraries anytime soon if I can help it.