vSphere provides a central management interface for the entire stack. In addition to application level redundancy, VM level redundancy is offered through HA and DRS.
Varnish sits as a secondary cache layer behind Akamai. Two servers operate in a Primary/Secondary configuration with failover managed by HAProxy. Requests peak at around 10k/s.
MySQL is the primary datastore, this is setup in a Master/Slave configuration, with offsite replicas.
Java powers the Escenic CMS used in the stack.
Tomcat provides a fantastic application container that runs the majority of services of the site.
Apache splits static traffic from application traffic, as well as providing a selection of tools to assist in running of the site (rewrites, logging etc).
Full text search is provided by a SOLR cluster. This is done on Master/Slave replication with Varnish as a cache.
Akamai sits at the front of the site, all assets and pages are cached for a minimum of 60 seconds. Requests to the edge peak at over 100k/s.
Memcache caches database results and articles, reducing overall DB load and allowing seamless DB maintenance during quiet periods.
HAProxy manages internal and origin load balancing using KeepaliveD. Two small servers host the entire site, never moving about 15% load even during the largest load spikes.