This tutorial explain how to speed up your Apache webserver with mod_deflate and mod_expire.
mod_expire controls the setting of the Expires HTTP header and the max-age directive of the Cache-Control HTTP header in server responses. These HTTP headers are an instruction to the client about the document's validity and persistence. If cached, the document may be fetched from the cache rather than from the source until this time has passed. After that, the cache copy is considered "expired" and invalid, and a new copy must be obtained from the source.
Like mod_gzip, mod_deflate allows you to compress files before they are served to the client, saving your server traffic.