How to install 100 server's less effort?

I am trying to install 100's of ubuntu servers,they needs servers(apache/memcached) to be configured and they needs some other packages(only 5 or 6) to be installed. what is the best way for this ?

If you're looking for some degree of automation on bare metal installation, there's Orchestra. For cloud, specifically the Amazon EC2, you can use juju for completely automated deployment.

Orchestra's Launchpad page is quite lacking on information and details, as of writing this answer. This Ask Ubuntu answer will explain, in brief, how it works and links to appropriate documents to get started on using it.