You might consider downloading the OSGEO Live DVD, which you can run in a virtual machine environment in case you don't want to install a bunch of stuff on your machine while testing it out. It comes pre-packaged with a bunch of different open source GIS software packages, including web mapping tools.
I also just attended a conference where they presented the OpenGeo Suite, which has a pre-compiled stack of OpenLayers, GeoServer, GeoExt & PostGIS. They offer both the "Enterprise Edition" (paid for version with support) or the "Community Edition" (free) versions.