Speaking of D3, Mozilla open sourced a library they use on top of D3 to visualize time-series data in a "principled, consistent and responsive way."
If you're serious about visualizations, you'll still want to learn D3 itself, but it's great when we can optimize and simplify common use cases. That's exactly what MetricsGraphics.js does. Here's a taste:
Check out all of the examples of what's possible here: