I have been playing around with a free opcode cache recently called XCache. I’ve been fairly happy with the performance gains, given the price and the cost of the competition at Zend. I love their ZDE and debugger, but their prices have always been an issue with me and the wallet. XCache is still being developed, but I’ve seen some nice speed increases on my windows development box, but have yet to deploy it to a production box. This sort of mechanism should be built into the language, but I’ll have to wait for a future version of PHP before that happens. At least JSON is now in the language by default.