Dori Smith at Backup Brain points us to the free Hetima’s SafariStand. You can view source of a web page and see syntax coloured text, change the text and see the changes reflected in the page. In that respect is a little like the wonderful Firefox Web Developer extension.
It was probably also Dori who put me on to the invaluable Saft (NZ$18). Although it has complex and annoying download and upgrade procedures it has some extremely useful features. I particularly like the way it restores whatever windows and tabs were open when Safari quit and the ability to re-order tabs.