I've talked about unlocker before, it's basically a fabulous little utility that tells you which app is locking your file (and it normally says it's the TortoiseSVN cache which brings me neatly onto my next utility...)
The code you produce at work is version controlled, so why isn't the code your make at home? TortoiseSVN is the best way of managing a home version control system as it's a really easy Windows Explorer plugin.
So you're developing a large application - and by large I'm talking tens or even hundreds of dlls.
You change the public interface on one of the non-dynmically loaded ones and, because you're in a hurry to get a build finished, only rebuild that dll.
Suddenly you can't start you app up any longer.
Dependency walker can tell you which other dlls need to be rebuilt so that they can interface with the changed dll.
You're not still using notepad to open .txt files are you?
Notepad++ is far better as it supports custom plugins and has macro recording, yet it still starts up in an acceptable time.
Of all of the freeware editors out there, this is my favourite as it behaves the most like Visual Studio when the Ctrl key is held down and your flicking from word to word.
Other alternatives to the Big Bad Pad are: PSPad or Programmer's file editor, but I've tried them both all I'm sticking with Notepad++.
Want to know what's eating all your processor time? Download Microsoft's pimped-up task manager, Process Explorer.
There is generally thought to be a 10 fold difference in productivity between poor programmers and expert ones. I believe that this is in no small part down to the experts' use of keyboard shortcuts. Auto Hotkey allows you to set up hotkey scripts to control virtually anything.