Check out this promising beta by ZingChart, HTML5 Canvas.
This advanced Zoom, Scroll, Preview is very well designed and implemented.
They also have sparklines, which are microcharts used to convey the “shape” of data, not necessarily all the details a full size chart would include.
ZingChart also offers a Speed Test example, which I think is pretty cool for helping non-super-techie people like myself understand which factors can influence chart loading times.
Other HTML5 Canvas Chart options
jQuery Visualize Plugin
Mobile charting libraries
04.Google Chart Tools
01. aiCharts v1.5
02. Java [TM] Charts for Android
01. Mobile Charts- a GUI for the Google Charts API
02. Drawing and Graphics with UIKit and Quartz (instructions) (Quartz demo) (Quartz2D programming guide)
03. SM2DGraphView (Cocoa)
01. PySChart v0.3
Windows Mobile specific
01. TMS Advanced Mobile Chart Warning- this may be the ugliest chart library I have ever seen; hopefully it can be styled
02. ComponentOne offers 2D charts for apps in their Mobile Studio
For Mobile devices that allow Flash, I would suggest browsing through these lists:
28 Rich Data Visualization Tools
List of Data Visualization Tools
75+ Tools for Visualizing your Data, CSS, Flash, jQuery, PHP
Please comment if you have found other charting options that work well for mobile sites and apps.