Sorry, I messed up. My configuration was substandard this morning. Upgraded the memory available to the WP & MySQL instances. Turned on WP-Supercache. And adding a Varnish layer in front.

Try W3 Total Cache, they have super-tight Varnish integration.

Working on it with vmfarms guys (we got 10x our high point traffic using hourly measure on this post) updating our infrastructure to be more resilient.

I recommend replacing super cache with W3TC. It has a lot more features, including minifying your CSS and JS. If you need help with it email me, dan at driverdan dot com.