In all versions of Windows, users will be able to notice a significant decrease in the responsiveness and speed of the OS. Despite consistent defrags and maintenance of the PC, the best way to get that PC as fast as possible is to perform a clean install of the OS. After clean install, Windows is ready to go. But to be a true power user, there are lots of programs that need to be installed before Windows is truly ready. All of these are free, with links to where you can find them yourself. If you tend to reinstall your software alot, think about putting these files on a CD or network shared drive. Almost all programs will need a update, but most should update themselves after install. For reference, the main PC I use is a Windows Vista, AMD 4800+ Dual-Core with 2GB of RAM, and these programs show little impact on the system.
Security should be the first set of programs installed. All the computers on my network use Norton Internet Security. While Norton products in the past have been ridiculed for their system resource use, the 2008 version of NIS doesn't seem to have a very big effect on the system. However, Norton is very expensive if you don't get it with a rebate. Paid-for security services, especially all in ones like Norton Internet Security and ZoneAlarm Internet Security (which is fantastic, probably better than Norton, but it's rarely offered with a rebate), are typically easier to use and provide adequate protection. If you're going the freeware route, which is just as adequate, you'll need two (at the least), Anti-virus and a firewall. Anti-spyware is also good, however most free AV programs have anti-spyware included.
Avast! Anti-Virus (Home Edition)- It's the best software that you don't have to pay for. It automatically updates on a schedule, and it has pretty good realtime protection. There's a drawback, however: you'll need to register the software to get a key that will allow you to use the program for a year. Also notable is that Avast! is a bit heavy on system resources, so if you're on a slow machine and you use a lot of resources playing games or designing, you'll probably hit a few snags. As with all programs, be sure you READ the file you are sending to the virus vault, as many times it turns out to be a system file you'll need to replace.
ZoneAlarm (Vista) (XP/2000)- ZoneAlarm is the tried and true firewall. Other users prefer Comodo, but the interface of ZoneAlarm is easy to use, and it gives you an easy to understand prompt when a new program requests Internet access. While the prompts are naggy at first, they go away if you click 'Remember this Program' in the box that appears.
Internet Explorer 7 is good. Compared to IE6, which is a decent browser but a horribly unprotected one, IE7 is amazing. However, tabs are a new concept to the IE team, and it shows when tabs are loaded in the browser. They are a bit slow and awkwardly inserted. A good tab manager is essential in a modern day browser.
IE7Pro- Since IE7 does come on every computer, you'll definitely use it with some protocols. Some programs launch IE7 to fill out information and such. IE7Pro makes IE7 much easier to use. The add-on makes the browser behave more like Firefox.
Mozilla Firefox- Firefox is easily the best browser around, with addons and extensions to make the browser more suitable to your liking.
Foxmarks Bookmarks Synchronizer- Foxmarks syncs your bookmarks across multiple desktops. You do need to register, but it's simple, and makes syncing with their server painless.
If you spend any time at all on the computer, you'll end up needing a music player, video player, and photo viewer. Windows includes Windows Media Player for music and videos as well as Windows Photo Gallery for photos, but both of those are adequate but not perfect. Here are some better programs.
MediaMonkey- MediaMonkey does an excellent job at managing your music. It's an excellent player, but excels at device synchronization. Also hidden among its many features is its ability to download and automatically sync podcasts. (Try the HotSpot and Buzz Out Loud for audio, and On The Spot and TekZilla for video podcasts.)
Windows Live Photo Gallery- It's a modest improvement over the default viewer, but it allows easy upload to Windows Live Spaces and Flickr (simple login required) as well as MSN Soapbox for videos.
VideoLAN Player- VLC will play pretty much anything with no problem. Of course, you'll need a codec pack for all the videos such as the K-Lite Mega Codec Pack. VLC is small and plays videos beautifully.
Also: GOM Player
Foxit Reader- You'll always need a PDF reader for brochures and user manuals. But Adobe Reader is slow, resource hogging, and very intrusive. Foxit is a very small but powerful reader.
7-Zip- When transferring big files (especially over BitTorrent), people have the urge to compress the files for faster downloading. It's a good idea, but you'll have to uncompress the files using the same method they compressed the file in. 7-Zip does most file types and, unlike WinRAR, is very small and light on the system.
When you go to make your download CD, be sure to include the latest drivers for your printer, video card, and sound card. While the printer's drivers will likely not be updated, be sure to pick up the latest video and sound card drivers off the manufacturer's site once you're set.
Popular driver sites: