total cache, super cache, most of them create static html versions of the page. Super Cache is a bit more clever in that it depends on htaccess instead of PHP code to check to see if the on-disk cached version exists. The benefit here is PHP module does not need to fire up -- apache can serve this very rapidly with little memory footprint.

I used W3 Total Cache. It generates a static file and puts it in apache's search path, so it never hits PHP