About
The deegree iGeoportal project is a web-based client that can interact well with Geoserver. From the iGeoportal docs:
deegree's iGeoPortal client is based on OpenGeospatial Consortium's Web Map Context, which defines map client status information. Apart from benefits of using an open standard, the employment of the Web Map Context specification eases the development of clients by relying on reusable modules and making extensive use of XML technology.
Configuration
The configuration of the iGeoportal client is somewhat difficult to configure at first, but everything necessary to get you started is outlined in the PDF documentation. The configuration files are mostly XML-based. The iGeoportal section also contains screenshots of the web client in action.
iGeoportal and Geoserver
Here is a screengrab of a iGeoportal displaying Geoserver WMS layers:
