Install ImageMagick with the php-pecl-imagick extension
Introduce memcached as part of a caching strategy.

Ideally we'll have another caching server when we move into production, so we might as well start planning around that now. In the meantime we can make sure the web server also has the rules from the cache server applied to it.
Switch to CentOS box provided by Puppet Labs

The CentOS box provided by nrel.gov included a preinstalled MySQL that upgraded to 5.1.69 during initial provisioning. To avoid having to remove that version just to install the latest MySQL 5.5, we're switching boxes.
Add Zend Opcache to PHP 5.4 for opcode cache
Add mcrypt and imap extensions for PHP