What is a "must have" application if I would like to build wordpress sites on my MAC OS X?

I’d like to develope websites, using the famous wordpress blog engine on my macbook (MAC OS X Leopard), and I am really curious what people are using to make great sites. I am not just thinking about Adobe photoshop, but more little apps that does something extra for you to make a nice and productive, useful site. Let me know what apps do you use, and if you give links that is also appriciated!