Which freeware / open source apps and utilities make your development life a little more enjoyable? Please provide URLs for anything you recommend.
Here's a brief list of some of my favorites:
Notepad++ is my text editor of choice, it has to be installed on any PC I work on.
Ditto is a lightweight and highly-configurable clipboard manager that I love.
7-zip for file compression, with command line support.
WinMerge is a fantastic file diff tool with plugin support. I even found a plugin to support Visual FoxPro's .VCX class libraries.