This looks pretty fantastic. New features for charting coming in OpenOffice.org 2.4.
and more here: http://wiki.services.openoffice.org/wiki/Chart2/Features2.4
To try it out, click here for the announcement and download info.
Here's just one of the new features, quoting from this post.
Now, it is possible to display the equation for a trend line (regression curve) next to it. The formula object can be moved around, formatted with a number format, font and graphical formatting.
Alternatively, or in addition, the correlation coefficient R² can be displayed in the formula object.