Features
Handles huge data sets: dygraphs plots millions of points without getting bogged down.
Interactive out of the box: zoom, pan and mouseover are on by default.
Strong support for error bars / confidence intervals.
Highly customizable: using options and custom callbacks, you can make dygraphs do almost anything.
dygraphs is highly compatible: it works in all major browsers (including IE8). You can even pinch to zoom on mobile/tablet devices!
There's an active community developing and supporting dygraphs.