JFreeChart

Allows creation of quick, simple Swing-based graphs.  I'm using this because I want to do some quick numerical modelling and validate the results.

Available in Maven:
http://mvnrepository.com/artifact/org.jfree/jfreechart/1.0.19

Vogella have a nice example:
http://www.vogella.com/tutorials/JFreeChart/article.html

Would recommend this for examples of specific charts:
http://www.java2s.com/Code/Java/Chart/CatalogChart.htm
http://www.java2s.com/Code/Java/Chart/JFreeChartLineChartDemo6.htm

In most applications you'd probably use web services and D3 or some other JS library.  It would probably be better to write your data to CSV and open it in Excel/OOffice.