Geotools is used by a fair number of projects both open source and commerical.
- GeoServer — OGC http://www.opengeospatial.org Web Feature Service (WFS) reference implementation
- GeoVISTA Studio — Codeless visualization and model building environment
- The Balloon Project — The Balloon Project http://theballoonproject.blogspot.com
- uDig — User-friendly Desktop Internet GIS http://udig.refractions.net/
Many of these projects have Screenshots available.