Couple with Firebug, you can log all your PHP method calls with FirePHP. Ideal tool for AJAX/JSON/XML Developer.

Gayadesign has released another helpful DIY script.  Powered by jQuery, you too can preload your HTML site as if it was flash. QueryLoader supports partial or whole website preloading. And best of all, it handles both <img> and css background image gracefully. Give it a go!