That being said, I looked through my start-menu and harvested every free app that I use. This is all quality stuff that's gotten some use, so look it over.
Note that I'm running XP. Some of this stuff won't be of much use unless you're running something NT-based.
Page File Defrag. The disk-defrag that comes with Windows works just fine. The only problem is that there are some files that it can't defragment, specifically the virtual memory paging file and the registry database (as they're both in use at the time). This gizmo will tell you if these files are fragmented. If they are, it'll set itself up to load itself on startup and will defragment those files before most of Windows starts. That's basically the only real advantage that "professional" defragment tools have over the one that comes with Windows, so this'll save you some money. The professional ones can also defragment your drive in the background while you work, but that's really only necessary if you've got an unattended server that does lots of database stuff (gamedev uses Diskeeper pro for this very reason). Get this.
AVG Free Edition. Every bit as good as the storebought antivirus tools, but it's free. Does all of the virus stuff that you need, including scanning incoming email attachments (in Outlook) and quarantining 'em if they're viruses.
Desktop Sidebar. It's really only useful if you've got two monitors, as it takes up a lot of screen real-estate, but it's a nice little dock for all kinds of desktop widgets. Google Desktop also has a sidebar, but I like this one better. It looks better and has more good widgets available for it. If you've only got one monitor, go with Konfabulator instead.
Google Desktop. Gives you the ability to google-search your own files. Check out their plugins section, as it's got plugins to search some stuff that you might want, like the plugin to search Trillian chat-logs.
IconTweaker. Good if you've got a big monitor. Lets you change your icon theme to something nicer than the Windows default, especially that XP supports arbitrary-size antialiased icons. Basically the same as that Stardock Icon thing, but it's free. The icon themes that come with it aren't so great, but you can download the WinCustomize ones and change 'em manually.
Microsoft Antispyware. Does the job. Is free.
ZipGenius. I've only been using this for a month, and the jury's still out as to whether this is as good as my old standby PowerArchiver. It appears to be as good and looks more like a part of XP than PA, so I'm sticking with it.
Startup Manager. Far as I can tell, this hasn't been supported in a while and you might need to jump around to find a working download, but this is still the best thing I've found to manage the programs that start with Windows. There are a half-dozen places where startup apps can stash themselves, and this one will show you all of 'em. You can add, delete, or temporarily disable stuff that starts with Windows. There are a dozen clones of this one, but I still like this one best. In fact, the startup manager that comes with System Mechanic is a virtual duplicate of this.
ActionScript Obfuscator. Honestly, I don't know how well this works because I've been using the commercial FlashEncrypt. It takes a compiled SWF file and messes with the code so that it can't be decompiled easily. A must if you've got Flash content that you don't want to show up on somebody else's site.
Acrobat Reader. You've already got this installed, so I don't need to say much more about it.
X-Fonter. The latest version isn't free, so you'll need to find an earlier version if you're a cheapass like myself (I'm using version 3.7.5). This is a great tool to organize, install, and uninstall fonts.
Media Player Classic. It plays just about everything (including Quicktime, RealMedia, and DVDs) and it's free. It's also dirt-simple to use, modeling its interface after an early version of Windows Media Player, before they wrecked the product with a million annoying skins and "visualizations".
Firefox. I'm not on the "It's a million zillion hojillion times better than IE" bandwagon, but it does do a few things better than IE, like tabbed browsing and PNG support. I use Google Toolbar for spell-checking and form-filling.
Opera. Basically the same as Firefox. It does a couple of things better and a couple of things worse, but they're so similar that they're almost indistinguishable. I've got this installed so that I can make sure my web pages look good on all of the major browsers. I'm using the version 9 beta because the "stable" version 8 kept crashing on my machine for some reason, most likely related to Java getting less stable with every release.
Yet Another Bittorrent Client (YABC). I don't bittorrent stuff all that often, but when I do I use this. It works very well.
eBay Turbo Lister. Honestly, I don't like this piece of software very much. It crashes more than it should, gives seemingly random warnings about listings, and requires almost constant "close and restart" updates to keep up-to-date with eBay's categories, but this is pretty-much required if you plan to sell more than about three items on eBay at a time and don't want to enter everything manually on a web-form.
Juice (formerly iPodder). I just noticed the name-change today, but it appears to be the same software. This is a really nice podcast subscribe-and-download client. You can schedule your downloads, it's got built-in bittorrent support (which is why I don't have iTunes installed). It's very unobtrusive (which is also why I don't have iTunes installed). And it can launch your downloaded podcasts directly. I've got no complaints at all with this thing.
Password Corral. Simple and useful. It's a little spreadsheet-type thingy that securely stores all of your passwords for you. One nice thing is that it's got the option to dump all of your password information into an encrypted text file upon program exit. That way you can save your password-list when you back up your machine.
NSIS. If your needs for installation are simple (and there's a 99% chance that they are), then look no further than this. It's small, easy, and works like a champ. No complaints at all about this.
JCreator. The free version is actually throttled to a small number of classes, but I haven't yet hit the limit, as my past Java projects have been small. This is a very quick and easy-to-use Java IDE. If you've ever had to slog through one of those Java-written Uber-Editors out there, you'll appreciate this immediately. It doesn't do as much as those (no GUI builder, for example), but if you just want to compile and test Java code, this is perfect.
PatchMaker. This is something from ClickTeam, makers of those gamemaker tools that C++ snobs all look down their noses at. It's a good tool for making standalone patch files. It's quite simple to use. You just give it your old files, your new files, and a couple other options, and it builds a standalone self-installing patch file for you. The free version pops up an ad for itself and the doesn't have as many options as the commercial one, but that doesn't bother me. I've had a PatchMaker-made patch for one of my old game packs on thecodezone.com for about five years now and haven't yet had a complaint that it doesn't work.