Every standard home computer should have either these programs or good equivalents. These are links, rather than archives, because there's no good reason not to get the latest version.
AVG Free (Antivirus - equivalents include Norton, Sophos, Symantec, McAfee)
Open Office (Office Suite - equivalents include Microsoft Office (Word, Excel, Powerpoint))
Spybot - Search and Destroy (Anti-Malware - equivalents include Lavasoft Adaware)
This is stuff you may or may not need, but I find it useful. Some of it represents old versions that I keep to use with Windows 98 (which I still use on those thankfully-getting-rarer occasions when I use Windows).
Birthday (archived) - reminds you when people's birthdays are coming up. Phil thinks it's inherently unstable - I think it just doesn't like ZoneAlarm myself.
DivX Bundle (archived) - the up-to-date versions don't work with Windows 98. Fortunately I found this on my hard drive. Allows you to play DivX videos and stuff, hopefully.
Leech FTP (archived) - an FTP program, basic but functional. If you don't know what an FTP program is, you probably don't need one. Will never be updated.
WinAmp Version 3 (archived) - think some people like this better than the newer ones - can't quite remember. I use it because it does its job.
Patches and mods and stuff for the ancient games that I still play on Win98 when it's working well enough (which it currently isn't).
Deus Ex Multiplayer Patch (archived) - the final patch released for this game.
Ever had Windows ask for a .dll file that was already there? In a situation where sfc isn't really an option? (Or fails to work) Ever gone looking for a replacement file, only to be forced to sign up for something and wait in some queue to download it? I have. All files probably Windows XP unless otherwise stated.
Stuff I've found useful at work.
APC Powerchute 7.04 - fixes a serious problem with earlier versions.
Cisco Aironet Site Survey Utility 1.2
MDB Viewer - deal with corrupt emails in Outlook.