Launch an external diff tool like WinMerge in Eclipse
EditBox is the Eclipse plugin for source code background highlighting.
Open-source plugins included in the distribution of IntelliJ IDEA
Literate programming for eclipse
a DSL for type systems, reduction rules, interpreters for Xtext langs
Eclipse integration for Isabelle proof assistant
An Eclipse plug-in for the IBM FileNet P8 Content Engine and CMIS
the disruptive IDE for COBOL developers
PL/SQL Editor module for NetBeans IDE