My favorite plugins for Eclipse : M2Eclipse for maven, Spring IDE, Subclipse for Subversion, Jadclipse to decompile classes, Java source helper and Properties Editor.
My very short list
M2Eclipse for maven
Resolves the project dependencies with maven, displays the tree of dependencies (why X.jar is returned), makes it easy to add a dependency to the pom by parsing the repository... Also provides a decoration label to display the current version of a project.
Autocompletion for classes, properties name and validation.
Subclipse for subversion
Subversion options with a synchronizing feature as a bonus : it prevents unfortunate commits to be done. Also "override and update" is useful.
Jadclipse for jad
Opens .class files with jad instead of the annoying "no source found".
Jora for Oracle
Avoids having a greedy Toad opened and provides much better and quicker auto completion (tables, fields). It has less features than toad but it is enough for my use and make the features accessible more easily (SQL History, oracle functions).
http://jora.luenasoft.de/updatesite or http://jora.luenasoft.de
Decorates classes that have tests and make you switch from the class to its test in one shortcut (Ctrl+J). I just wish there were also a shortcut to run the test even when we are on the tested class.
http://moreunit.sourceforge.net/org.moreunit.updatesite or http://moreunit.sourceforge.net/