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.
