After doing a long and tiring search, I've found that Panic's Coda is by far the best web editing application. That goes not only for Macs, but in general.
http://www.panic.com/coda/ (5/5 Stars)
Highly, highly recommendedWYSIWYG is great, but I still like to code by hand for two very strong reasons: 1) It cuts down drastically on the amount of extraneous, unneeded code. 2) It gives you the power to manipulate your site's content much more in depth for personalization and dynamic content.
Here are just a few reasons why I love Coda:
1) It's damn sexy. If you think BBedit is the ideal text editor, welcome to the 21st century. This thing is absolutely fluid in the GUI and has a very intuitive interface.
2) It has a built-in preview tab. You don't need to launch Safari on the side.
3) There's a built-in CSS editor. It detects all pre-existing CSS styling code in a web page and shows each style in a graphically-friendly editor. Using visual drop-down menus, you can see in real-time how each style is being manipulated. Also, there are a few nifty CSS style options that I didn't even know existed until I used Coda.
4) Built-in FTP file manager. When you edit documents locally on your Mac, a "Publish" button appears on the bottom of the app to transfer all modified documents to your FTP server. No more keeping track of changes you've made. Coda also displays a list of each file that's being uploaded during a publish, so you can remove a file from the list if you don't want it to transfer.
5) Flexible workspace windows. You can divide your workspace to include an html editor, preview pane, css editor, or whatever configuration you desire. Each pane simultaneously gives you different perspectives of the same open document. It's great for using the css editor and html editor while previewing the changes all at the same time.
Download it to see what I mean. This is an awesome app. Everything seems very well thought-out.