There's actually quite a lot of free software out there, far more than I could possibly cover. So I'm just going to talk about a few applications that I know personally. I figure with any luck at all, a lot of suggestions will appear in the comments.

First up, a recent discovery for me; Seashore is a simple, easy to use and surprisingly full-featured image editor. It supports layers, channels, tools, including textures and brushes, and is perfect if you mostly want to do Save As from .png or .jpg or .tiff, including transparent .gif, and image scaling, by percentage or pixel. There's easy to use documentation embedded in the Help system.

Next, one of those programs that I use all the time, and have used for years; Textwrangler from Barebones Software. I love these guys; when I first started learning HTML way back in 1997 is used their free text editor, BBEdit Lite. TextWrangler is the still free but much more studly cousin of BBEdit Lite. Basically, TextWrangler is a full fledged text editor plus; it lacks some of the special ease-of-use-tools of its sibling BBEdit Pro (I heart BBEdit Pro), but unless you're writing a lot of Perl, or PHP, or HTML pages, then you'll be more than happy with TextWrangler, which you can download, absolutely free, right here. TextWrangler has complete support for GREP, as well as the usual high-end-search-and-replace functions, you can directly SFTP and FTP from it, it automatically converts ASCII and to high ASCII and the other way 'round (turn those "curly" quotes back to straight, or vice versa, and em-and en-dashes, too). You can change case with pretty much any option you'd ever want, right from a menu. You can do things like compare files with the Unix Diff command. Plus it does color-coding of syntax, which, if you create HTML pages, or write any sort of code at all, you want. It's got sophisticated text abilities, and makes a surprisingly pleasant environment for just plain writing. You might not know you need it, but trust me, you do. In a lot of ways, it's the perfect word processor for people who just want to write text and don't need formatting beyond paragraphs. If you want a minimalist word processor, take a look at Bean.

Bean is a Word processor that's somewhere between Apple's own rather nifty TextEdit, and MSWord. It's absolutely not a substitute for MS Word, but it is full-featured in that you can use templates, spell-check, a thesaurus, fonts, styles, images, etc. What I like best of all is that it's a clean easy-to-use stripped down interface that not only gives me a constant live, always visible word and character count&mash;it saves in pretty much any file format I'd ever want; .rtf, .rtfd, Web Archive, MS Word, and Web archive. Export functions include .pdf, pretty usable HTML as well as MS Word, among others. While I mostly favor Bean for the fact that the UI gets out of the way and lets me write and track word count, I very much like that I can compose a document in Bean, then send it to Email.app. You can change the background/text colors, and use Styles astonishingly easily to copy a paragraph or text style to another. Bean really is a lean usable word processor; it doesn't do predefined styles, or footnotes for example, but if you just want something that helps you write and otherwise stays out of the way, Bean is definitely worth a quick look; you might find it as useful as I do.

I use Blacktree's QuickSilver every single day; I don’t even think about using it, until I’m on a Mac that doesn’t have it, and then I miss QuickSilver enormously. QuickSilver is a tiny program that lurks in the background until you need it; you summon it forth with a quick key combination (I use Command-Space; you can assign whatever you like) and you can launch any application, iTunes file, Web bookmark or URL, script . . . the possibilities are pretty much endless. And I’ve barely scratched the surface of what it can do; more sophisticated users have found all sorts of ways to use QuickSilver to save time, effort and keystrokes. Don't worry about the "beta" description on the site; this application is frequently updated and has been in beta for years. It's worth at least glancing at the tutorials.

If you want an HTML editor and aren't terribly comfortable hand-coding HTML, take a look at Mozilla's free HTML editor Nvu (pronounced n-view, short for "new view"). It's got a bit of a learning curve because the interface is a bit different, and still a little rough around the edges in terms of consistency, but it's actually quite powerful, and it includes some decent tutorials in the built-in Help files. You can edit multiple pages at once with tabbed editing, it has built in graphical support for Tables (resize by dragging), and a full CSS editor. You might be especially interested in knowing that FTP is built right into Nvu. I'm going to assume you already use or know about Mozilla's Firefox, and that you at least know about its companion email client Thunderbird; if Apple's Mail.app isn't for you, you might find you like Thunderbird.