Text Editors:
-- Coda (by far my favorite, probably the best known Mac editor. It isn't WYSIWYG like Dreamweaver though. It allows you to do a variety of web design tasks all in one interface, including the coding, css editing, previewing and FTP.) http://www.panic.com/coda/
-- Textmate (Another popular coding app. Quite powerful. Code only, no WYSIWYG)
-- free code-only options are Smultron and TextWrangler
WYSIWYG Editors:
-- Dreamweaver (obviously)
-- Rapidweaver (based primarily on templates, so if you do the coding yourself, this may not be the way you want to go) http://www.realmacsoftware.com/rapidweaver/
-- Freeway is another WYSIWYG tool, though it seems on the expensive side. http://www.softpress.com/
-- Sandvox http://www.karelia.com/sandvox/
Misc programs:
-- Cyberduck (FTP, Free)
-- ForkLift (FTP, about $20, my favorite FTP app)
-- MAMP (Apache server, PHP, PHPMyAdmin - let's you work with databases and use the PHP programming language)
I've only personally tried the code editors and dreamweaver -- I tend to stay away from WYSIQYG editors, since I'm not confident they'll generate clean, quality code for me. They can often create good looking websites, but are limited to certain styles and/or the code isn't good quality/has issues displaying across different browsers. As far as I know, all of the tools above have free trials, so make sure you try the apps out and make sure you like them before you buy.
If I didn't include the URL, a quick web search should turn it up.