I use open source/ free stuff.
Textwrangler for editor. Cyberduck for FTP (Cyberduck is specifically designed to work with Textwrangler!).
There are free wysiwygs - I tried Nvu and Smultron. But I realized that it was taking me as long to learn them as it was to learn the code, so I just started writing the code in Textedit, then Textwrangler. I highly recommend that you just learn to code and forget about wysiwygs.
I did finally pay for one app - TextExpander. You assign a keyboard shortcut to a code snippet and it inserts it. Type ,D and you get opening and closing div tags with the cursor placed between them. It saves an incredible amount of time and typing.There are other apps that do this also but no free ones that I could find. However, On Snow Leopard you can create keyboard shortcuts like this right in the OS. I haven't used this method yet though.
wordservice is a great little free app. You can do various text manipulations like change the first letter of all words or the first letter of all sentences highlighted into caps, for instance. It really comes in handy when doing any kind of writing. Some of these things ( but not all) can now be done through settings in the 'services preferences' menu of the Snow Leopard OS.
'Preview' now allows you to do full web optimization processes to jpgs. 'Grab' gives you a very good onboard screengrab utility.
for fancier graphic manipulation there is a Mac version of XNview, and also the Gimp. I use both. (No cracked versions of photoshop etc. for me!)
versiontracker and macupdate are great places to find open source, freeware, and shareware.
For fancy coding there is Aquamacs. I have it installed but have never actually used it however. It is a gui for Emacs and has a fairly steep learning curve. someday I will find the time.
Don't forget Firefox and the Webdeveloper plugin. This is a tool I can no longer do without. Everything from page validation to a color picker.
localhost is available out of the box. Go to system preferences/sharing and check the 'web sharing' box and you've got an apache server. put a file titled index.html in your 'Sites' folder and you've got a local website to view your html pages on.
Get an Os X 10.6 manual. David Pogue writes an excellent one. There is a lot of software that comes with the system now which does all the things I used to have to install third party apps for. For instance I had 'Downloadcomment', to insert the url that a file was downloaded from, into the metadata. Now safari does this automatically - find it in the 'show info' window.