I really think that describing the software I use everyday (not the programming tools -- Delphi almost invariably -- nor what runs my servers, that's for another entry) tells a lot about me. I use very little from Microsoft, beside the OS. I like open source software, but I use also proprietary ones. I won't provide links to all of the programs, a simple search on Google will help you find them. So here we go.

• Operating system. My main computer, a Dell Latitude laptop, runs primarily on Windows XP. I have VMWare boxes with Linux. I also have Win3.1 and even DOS + Win 1.01 installed for demos. All my servers have Linux installed (mostly Debian), but that's for another time.
• Browser: Firefox. I've used tabbed browsers since Opera started working OK. Smart, fast, nice incremental page search, great JavaScript debugger and DOM Viewer... I could go on but will stop here. Plugins include the Google toolbar, Web Developer (superb!), and User Agent Switcher (nice to fool ASP.NET sites). I don't have many because looking for the best ones takes time. Suggestions?
• Mail: The Bat. I'm not so fond of it anymore, but have hundreds of filters in place... Moving mail, mailboxes, rules and all to a new computer takes second (ever tried with Outlook?). I'm considering a switch to Thunderbird or moving everything to GMail. I also use Spamhilator to protect some of my accounts.
• Newsgroups: XanaNews. Coming from Agent, it was a natural fit. It is written in Delphi and the full source is there. Don't plan switching for now.
• OpenOffice: most word processing and slides I do are based on this great tool, and have been for the past 3 years. And I have custom programs that hack the XML-based file system as well. Plus you get PDF and Flash output (for slides). And dictionaries for all languages. And lots of goodies. I still use MS Word (97!) as this is what my publisher requires and they have tons of macros that don't run in OpenOffice.
• Text Editor: Context. Very nice, written in Delphi. Good syntax highlighting for many languages. I also use XmlTypist an XML editor I wrote in Delphi (more on it soon, I hope).
• Imaging: InfranView and Picasa for viewing images, photos and the like. I keep switching from one to the other. Plus 20/20 for screen captures. Plus GIMP or an old PaintShop Pro for the rare graphic processing I have to do.
• Video: I have the full set of audio/video players (Real, QuickTime, Media Player, DivX Player).
• Music: iTunes for managing my iPod.
• Phone and IM: Skype: this is a software I use and like a lot. And is written in Delphi as well (possibly the most widespread Delphi app ever, with 209 million downloads!). Plus GMail Notifier.
• Firewall: Kerio is quite a good one. Nice that you see when Windows calls home (and can stop it)!
• VCS clients: Tortoise CVS and Tortoise SNV.
• Files/folders comparison: Beyond Compare. Outstanding (and written in Delphi).
• File transfer: WinSCP3: That's for SSH-based file transfers to Linux boxes I own.
• File compression: WinZIP. A classic.

Not that I claim these are the best tool in each category. They work. They are cost effective not only because most of them are free, but also because they help me get my job done without too much hassle. I rarely invest time to test something new (I'm too busy and too lazy!), but I'm open to suggestions...