Update 2018 This library hasn’t been updated since 2012. The underlying Raphaël framework has gotten some love in 2017, but although not exactly a replacement, Raphaël’s typical usecase of drawing vectors has been largely been overtaken by d3.js.
While having used Highcharts (a non free as in speech toolkit), Flot (reasonable, but Canvas based and thus slow in IE), and Visualize (semantically perfect as it reads from a table embedded in the page, but is more a concept than really fit for production) in the past, I’m still looking for an even better solution that is hence fast, is or can easily be made into reading html-tables (no separate array or hash of values) and without restrictions (free as in beer and speech; I’m a programmer). Note that I haven’t tried to connect tables and gRaphael yet…
Aside from the semantic correctness, however, gRaphael’s approach is really low level, and even basic things like grid lines aren’t implented by default. This is OK if graphs aren’t for print, but if they are you’ve got to build your own custom solution. Together with Raphael this can be done, but for your basic graphing other solutions offer this functionality out of the box.