I also just attended a conference where they presented the OpenGeo Suite, which is a stack of OpenLayers, GeoServer, GeoExt & PostGIS. They offer both the "Enterprise Edition" (paid for version with support) or the "Community Edition""Community Edition" (free) versions. (Update) OpenGeo Suite is now Boundless Suite.
Another package that was demonstrated at the conference was GeoMoose, which is a stack of MapServer and OpenLayers.
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.