One of the better threads I've seen anywhere for a while. Thanks for all the contributions. I'll add a few of my own Windows favorites. I'm heavier on the Linux side, but the funny thing about Linux is you have to add a lot less to a standard CentOS or Ubuntu installation in the way of tools - many of the good ones are already there...
Revo Uninstaller (Freeware version) - this is great for digging out stuff that tends to leave a lot of junk behind, stuff that often fouls up reinstalling the same software later.
All the SysInternals tools - while I liked them more before they adopted by Microsoft, these tools are still huge. PageDefrag and Process Explorer are the biggies, but many of the others can be very useful in more defined circumstances.
Back|Track - hacker Linux tools collection on a bootable ISO. Like money, it's not what it is, but what you do with it, that defines it. I hope you will go the 'white hat' route.
WireShark - amazing network monitoring tool, and very useful when you're trying to figure out where your connection from client to server is hanging / freaking out / freezing / what-have-you.
There are others, but these are the ones I've got off the top of my head.
best regards - Mike
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