I use xcharts, It's very simple, good looking and based off of D3.js http://tenxer.github.com/xcharts/
they look nice, but do they support tool tips?
4th example demonstrates tooltips: http://tenxer.github.com/xcharts/examples/
Google charts is noticeably laggy at around 200+ data points. You can take a look here.
https://www.google.com/finance
HighCharts/Stock is magnitudes faster.
https://developers.google.com/chart/
[EDIT] Changed to charts and included link