I have used Epoch[0] and Rickshaw[1] before for similar purposes, and have heard that Plotly works well too (especially if the process that is generating the data is Python-based).
For simple line charts, maybe Smoothie[2]?
Currently, I am trying to make a dashboard for visualizing many different data sources with WebSockets and Chartjs but it's still not quite ideal-- there's a bit of lag, and sending too much data via JSON really slows things down. If anyone has solved that this problem I would appreciate it if they told me how they did it.
0. http://epochjs.github.io/epoch/