Antivirus & Malware Tools

AVG Antivirus - Offers a free version. Great software
Avast Antivirus - Offers a free version. Great software

Disk Utilities

Defraggler - Windows Defrag is horrible and slow. Great replacement. Made by Piriform... great company!
HiJackThis - Advanced User Tool - You can really mess your PC up with this tool... as well as fixing it... :)
CCleaner - AKA Crap Cleaner - This tool cleans up your system junk and your registry. Another must have Piriform program!

Windows Updates

Microsoft Windows Updates - MUST be using IE to do Windows Updates!

Misc. Downloads

LogMeIn - Remote access software. Log into your PC from anywhere with an internet connection.