Guides on server optimisation?

[JohnK]

Are there any good guides out there that anyone can recommend for optimising apache and the server in general to give better performance and load times to users? We have things like zend and ioncube installed so if anyone can recommend any other pieces of software such as those as well it would be cool.

Maybe we can compile a good list and guide here for all powervps users? :)

Thanks in advance,

John K