Memcached

Memcached is a service that allows entire database tables to be stored in memory, drastically speeding up queries to those tables and alleviating database load.

Guides to install:

http://www.if-not-true-then-false.com/2010/install-memcached-on-centos-fedora-red-hat

http://www.lullabot.com/articles/installing-memcached-redhat-or-centos

http://www.zayinkrige.com/installing-memcached-on-ubuntu-10-04