In this new post to the SitePoint PHP blog Akash Mehta talks about a web application, PHPBench.com, that runs real-time benchmarks comparing some of PHP's own structures (like for versus foreach or echo versus print).
The benchmark suite covers all the usual bases, taking a simple task - like iterating over an array - and speed testing almost every possible way to achieve it. Most importantly, however, Chris takes raw numbers out of the spotlight and instead focuses on how the options compare with each other.
Since the results are generated live, they'll change a little bit each time the page is loaded. Each also includes a link to the code behind the benchmark so you can test it on your own system easily.