Highcharts is really awesome. If you need to neat looking charts, this is the answer.
I faced a bit problem with setting the X Axis date format to stick with Month-Year format. That is because Highcharts automatically adjust the best possible date range. To maintain the date range to monthly (Month-Year format), is by using tick interval configuration.
To get monthly date range, set the tick interval to approximately one month, so the value is: 31* 24 * 3600 * 1000.
If Highcharts' Licensing does not fit you, then take a look at jqPlot. Not as fancy as Highcharts, but in my opinion it's the best for totally free js charting solution.