Chris A. a11n

This plugin requires PHP 5.3 or later, please check with your web host if you’re unsure.
Adoption uses the timezone that is set in the WordPres admin panel. Ensure you have set your local timezone in Settings > General.
Features:
<ul>
<li>Displays a bar chart with registration statistics for predetermined time periods (e.g. this week, last week, last 3 months, last 12 months, etc.)</li>
<li>Displays a “Quick Statistics” section which includes a summary of user registrations for popular time periods.</li>
<li>Easy to use, tidy and fits in with the overall WordPress user interface.</li>
</ul>

Adoption

Adoption displays user registration statistics in a neat dashboard widget

jvrtanoski

Plugin that will allow the blog authors to add simple but effective geo-chart, bar-charts or line graphs in their blogs. 
The plug-in provides shortcodes for each chart type. The short codes can be placed anywhere in the text of the post/page 
and the plug-in will render the chart in the place of the short code. The data for the chart is placed in form of table 
insite the shortcode tag. For more details see the samples in the FAQ section. 
The charts are based on Google’s Javascript charts library, and the format of the data table is determined by the library itself. 
For more details see the help pages of the Google Chart library.

GoogleGraph

Plugin allows the blog authors to add simple but effective geo-chart, bar-charts or line graphs in their blogs using Google's Chart .js library.

Adoption vs GoogleGraph