ProtoChart is a new opensource library using Prototype and Canvas to create good looking charts.

Features

    * Line, bar, pie, curve, mix, and area charts available
    * Multiple data series on same graph
    * Highly customizable legend support
    * Customizable grid, grid border, background
    * Customizable axis-tick values (both x and y)
    * Supports: IE6/7, FF2/3 and Safari
    * Even works on an iPhone!