Caching PHP scripts (intermediate opcode) in memory can make dynamic pages load fast and exert less load on the server resources (primarily the CPU usage). Typical PHP caching engines and accelerators are Zend, eAccelerator, xCache and APC (a PECL extension). Here’s a nice tutorial on APC-driven caching. Also checkout the very useful VPS MySQL and Apache Optimization Guide. Now top it all up with memcached, a distributed memory object caching system, and you have a pretty scalable LAMP architecture.