Cyberduck - Mac - A free FTP program. Very versatile.
Qumana - Mac - A free blogging application. Can work very well, but only after you've gone through some set-up processes that can be confusing.
OpenOffice.org - Mac/Windows - A free alternative to Word (Works just as well). Useful for writing posts.
Dictionary - Mac - An application that comes free with Leopard, which has dictionaries to multiple sources and even a thesaurus.
Writeroom - Mac (Windows?) - A free writing tool that provides a black background and space to type, taking away any distraction.
Think - Mac (Windows?) - A free app that isolates applications (like writeroom does when writing something) to keep you focused.
NewsFire - Mac - A free, and great, RSS feed subscriber/reader.