Are there any tools available to log the page load time for a php site?
Mainly looking for something that I can see trends of load times over time, I was considering dumping them into a file using error_log(), but I don't know what I could use to parse it and display graphs
Use the Firebug extension for Firefox, it has a Net panel that shows you load times.
If you want to do load testing, apache comes with a utility called apache bench, try ab --help in a console window near you.
See PEAR Benchmark. It allows you to add benchmarks into your code. You can have it dump an HTML table on your pages, or you can loop through the data and write to a log file.