Thanks to a contribution by Stephan Schwiebert, the Eclipse GEF Zest toolkit now contains an SWT-based tag cloud visualization component. Using SWT widgets and JFace viewers, you can create tag clouds like this one:
The tag clouds are highly customizable. To demonstrate the possibilities, Cloudio contains a sample RCP application. It can load a text file, provides access to the visualization parameters, and supports image export:
Cloudio is part of the Zest Git repository. Its help content (like the other Zest documentation) is generated from the Eclipse wiki. Builds and p2 repos are available from the nightly and integration CI jobs. Integration builds can also be installed from the marketplace. You can get in touch in the GEF forum and report bugs on Bugzilla.