The mod_deflate module provides the DEFLATE output filter that allows output from your server to be compressed before being sent to the client over the network. Learn how to enable it through yout .htaccess file.
If you have compiled apache with mod_deflate then you can potentially reduce your bandwidth usage by anything between 50% to 80%. Simply add the code below to your .htaccess file. Once done, you can enter your domain name at whatsmyip.org/http_compression/ to ensure it is working, and to see the bandwidth savings!