JMoney is a personal finance (accounting) manager written in Java. It is built using the Eclipse RCP and can be extended using plug-ins. If you wish your accounts program could do something that it cannot then download JMoney and write a plugin.
A plugin for the Eclipse IDE implementing NumericalChameleon: a powerful numerical convertor, supporting more than 2300 units in 78 categories (physics, radixes, exchange rates, unicode, etc). Fully integrated in the Eclipse IDE (refactoring, copy/paste)
EclipseQuote is a plugin for the Eclipse IDE that allows one to monitor a portfolio of stock quotes. It works by displaying stock quotes in an eclipse view. New stocks can be added, and prices updated, with one click.
TooShare is a stockmarket analysis tool. It is a platform whose design is based on Eclipse Technology architecture which permits extensions via plugin mechanism.