I'm surprised no one has mentioned JQPlot yet. I'm not entirely sure it will do everything you need, but it's a very, very capable library. It's in jQuery, just to note.
Demos of JQPlot here
JQPlot can fit all your needs, it seems:
- Line Graphs JQPlot supports these just fine, as you'd expect
- Histograms Histograms are just bar charts, so that should be ok. A colour histogram would just consist of
1px wide bars
- Scatterplots Scatter plots are also fine
- Motion Charts I think you mean bubble plots, which JQPlot also does
