There are so many useful Java frameworks and utilities out there, those are free and open-source . Here are a few of my recent favorites. Feel free to add your own to the list.
Joda Time : Java Date/Time replacement
Rome : Java tools for parsing, generating and publishing RSS and Atom feeds.
GWT : Java-Ajax web framework
Java Mozilla HTML Parser : A wrapper around Mozilla’s HTML Parser
JFreeChart : JFreeChart is a 100% free Java chart library that makes it easy for developers to display professional quality charts in their applications.
Lucene : High-performance, full-featured text search engine library written entirely in Java.
PMD: One of best code review tool with eclipse plug-in.
iText : This library contains classes that generate documents in the Portable Document Format (PDF) and/or HTML.
GanttProject : GanttProject is a project scheduling application written in Java and featuring gantt chart, resource management, calendaring, import/export (MS Project, HTML, PDF, spreadsheets). more info http://ganttproject.biz
XStream : A simple library to serialize objects to XML and back again