As I mentioned simply using d3 should be good enough. I have not found a chart library that cleans up after itself. You can take a look at the "basic charts" section: https://github.com/mbostock/d3/wiki/Gallery
flot is nice, at least for real time updates on charts. I'm building a websockets enabled realtime dashboard with flot, left it running last weekend, did not leak a bit.
Flot actually leaks quite a bit. We use flot at work and I had to hack the code to keep it from leaking. It doesn't leak as bad as NVD3, but it leaks. You will see it never surrenders the canvas element if you call shutdown on it if you check out memory snapshots.
The opposite for this are which?, ie: For people with not enough experience could be good idea to know which ones are bad in this regard and wich ones are good.
I`m in the hunt for a chart library. So far, I think in Google chart and highcharts.