For those times you need to add advertisements, alter length, reduce size, merge effects, or any other audio-related work, the free app Audacity will make the task simple.
By now, if you haven't heard of GIMP, then you've been living under a rock. This free program (requiring X11) allows designers to author (or alter, as the case may be) graphics, whether its an overall site design, a logo, or a banner. If you aren't running X11, then download Seashore instead.
Cyberduck, for all your FTP needs! Sorry, couldn't help myself. This nifty little app is open source and the ideal program for anything FTP, SFTP, WebDav, and more. Aside from its awesome file browser, the many integrated editors it has allows users to easily alter and edit information without hassle.
For those times you just want to get done, the project is small, the priority is low, and, as always, your time is too precious to waste. Nvu is a free WYSIWYG (what you see is what you get) app like Frontpage and Dreamweaver.
A nice plus about this app is that it works alongside the above-listed Cyberduck program. Smultron is a text editor, only more so, as it boasts tabs for multiple documents, as well as the always-welcomed varied text colors when programming.
Before you can get down to the fun part--writing, creating, and ultimately publishing, the webpage--you have to design it. Of course, good customers make this process much easier, but still, its not always fun to figure out the optimal design, and that's where Freemind comes in. You can use this program to connect, organize, and pattern your thoughts and ideas as they come, organizing them with the expanse of tools available.
7) Sunrise Browser
The Sunrise Browser was created specifically with web designers in mind, and offers features that may find useful, a few of which are: the ability to highlight and right-click text and perform a search using a user-specified engine, the ability to open web page source in a user-specified text editor, and snapshot entire web pages to save in GIF, JPG, PNG, or even highest-quality TIFF formats.
Blender is a powerful 3D model and animation program. Free, and with quite a following, this program can be used to create short animations, or to model 3D objects that be either be mapped en program, or with different rendering software.
9) CC Publisher
If, in the process of creation, you make something that you decide would best fit into the Creative Commons world, CC Publisher makes it simple to add your content (graphics, audio, video) to the online library for all to access.
10) xChat Aqua
For those times you need to do some last minute collaboration with your client, associate, or maybe just waste time, xChat Aqua is a 'powerful' IRC application that allows you to hold multiple chat sessions all organized into a neat series of tabs.
You're not doing all your work just to have it lost/edited/corrupted when your kid brother decides to toy around in your machine. To keep your system (and thusly, your data) safe, Multialarm will basically put a sound system alarm on your computer to shrill whenever someone uses it unauthorized.
Whether you're a beginner or an advanced user, the quality app YourSQL will allow you to mange your SQL database with ease. Features include the ability to fully adjust the interface to your needs, an import/export feature, UTF+8 support, and much (much) more.
Its always nice to have a video transcoder on hand, for those times you need to make put up a Flash video but only find MPG's on your hard drive. ffMPEGx is free, simple to use, and did we mention, free?
GIMP is an excellent program, but its definitely not a vector editor/creator. Inkscape is a free program very similar to Xara and Illustrator, making it inexpensive for web designers to create icons, banners, or other vector related graphics.
15) Q Emulator
As sad as it may be, sometimes you just find the perfect app on Windows and no equivalent on Mac. When that happens, Q Emulator allows you to run those apps at (almost) fullspeed.