The most important programs and plug-ins out there.   Free/nearly free for home use unless noted.

Antivirus AVG - Free Antivirus Software for the home (Ongoing Virus Protection for your email and web browsing)
  Trend Micro HouseCall - Free web-based virus scan for your computer.  (This is good to use to SEE if you have a virus, but installing AVG for ongoing virus protection is recommended for ongoing protection!)
Media Search  Kazaa Lite or K++ (Google Search) - These two variants of Kazaa are free from advertising and are ideal for searching for music / software / videos
  Emule - Another good program for searching for movies / software / music
  Google Image Search - Best tool for finding images
  Bit Torrent - Excellent tool for downloading media from WWW.  Expect this "swarm" form of downloading to take off in near future!  (Google Search for Bit Torrent Files)
  Search - GREAT text searching utility.
Anti-Advertisements Google Toolbar - One feature of this toolbar is a near-perfect popup blocker! (Will not work with AOL)
  AdAware or  Spybot  - These two programs find and remove programs that spy on you and/or create popup advertisements on your computer.
  Spambayes - The primary program here is a plug-in for Microsoft Outlook that intelligently learns to block popups.  Setup may be a bit complicated for non-computer type people, but once installed, this program will block up to 95% of email spam!
Image Viewing Irfanview - This is the best free image viewing program out there.  I *highly* recommend using it over Internet Explorer for viewing pictures!
Unzipping Files Winzip - The widely supported program to unzip files.  (Windows XP can unzip files without Winzip, but I still recommend installing it.)
Audio Winamp - The best software to listen to mp3's and streaming radio stations (Shoutcast)
The BEST plug-in's ETC... Shockwave and Flash - These two plug-in's for Internet Explorer are required to visit many websites.  (Games etc...)
  Acrobat Reader - This plug-in for Internet Explorer is helpful to view PDF files.
  Nimo (Google Search) - This is a one time download that allows many different video and audio types to be played on your computer.
  Quicktime Alternative (Google Search) - This is a replacement for installing and using Quicktime; Allows window to be expanded fullscreen!
  Real Alternative (Google Search) - Same as above, but replaces Real Player
  Crazy Browser - Incredible modification of Internet Explorer.  Allows you to browse the Internet with tabs, save groups of homepages, etc... Fullscreen mode has autohide navigation buttons.  Built in popup blocking also... See "Advanced Options" to realize the full power of this program!
  Google Toolbar - As mentioned above, this plug-in blocks popups, but also allows for easy searching of web pages, images, discussions, etc...  This is a *must-have* for Internet Explorer!  (Will not work with AOL)
Specialized Tools / Advanced Tools
Newsgroups Newsbin Pro - Advanced program for searching newsgroups for music / software / movies / pictures (Not free!)
  SmartPar - A program used in conjunction with newsgroups for reassembling missing parts...
  QuickPar - A program used to reassemble PAR 2.0 files.
DVD Tools Daemon Tools - Allows images of CD's / DVD's to be run from hard disk.
  DVD Shrink - Shrinks DVD's to fit on DVD-R
  BurnAtOnce - Freeware CD/DVD burning GUI