Is there any real alternative to GeoServer as dynamic map generator in Java?
Make sure to check out MapServer.
Both MapServer and GeoServer support OGC-compliant WMS requests, so they're basically inter-exchangeable if you use something like OpenLayers.
MapServer's got a handy installer that lets you install every aspect that you might need to get your server and web application going. It runs on Apache, which I find a big advantage over GeoServer, which runs on Jetty (it's all-java).
However, I'm now using GeoServer myself now. It's really easy to administer stuff via its web interface, and overall it just feels pretty polished. Maybe it's because I've been using it for a while now, but I just get stuff done quickly with it.
Take a look at OpenMap. It is a descent alternative to manipulate/display geospatial data.
The thread may be old but in case anyone else is looking for a similar solution it is worth checking out Nasa World Wind.
http://worldwind.arc.nasa.gov/java/