What are your tried and true utility applications? Free or pay?
Free
Ad-Aware- Weak but sometimes effective at dealing with various spyware issues.
Spybot Search & Destroy- Slightly stronger than Ad-Aware. Has some interesting and reasonably effective blocking agents. Agents can be a pain on rare occasion. I like to use Ad-Aware in tandem with Spybot.
CCleaner - A great utility for cleaning a system up without screwing it up. One of my foavorites.
Picasa- A great photo utility from Google. Works well, easy to use, but by no means a power house.
Microsoft Windows XP Power Toys-
Image Re-sizer. Awesome little tool that integrates into the right click for easily and quickly resizing images. Good for the quick and dirty, but would not want to use it on something where the re-sized image quality was paramount.
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Microsoft Calculator Plus. A better version of the original MS calculator included with Windows. A nice though limited converter tool is integrated into this version.
WinDirStat- Great utility for visualizing what takes up space on your hard drive(s).
7-ZipLong ago this replaced WinZip as my default file compression and decompression solution.
VLCA decent viewer that seems to be able to handle about every format on the planet.
Pay
FolderMaker- A handy solution for making folders pop with little or no effort.
Executive Software Diskkeeper- Best defrag I have yet encountered. XP only.
Nero- Best CD/DVD burner I have encountered. Not made for copying protected media.
RoboForm- Required when not using Opera. Fills in forms better than anything out there including Opera and FF.
ESET NOD32 Antivirus- Replaced AVG. Faster and better design than AVG.
ZoneAlarm Pro- Best firewall I have used. I however have not had any need to use it for the past year or so.