Mac: If you're a command line junkie, you probably spend a lot of time cd-ing into a directory every time you start up Terminal. Free plugin OpenTerminal opens a new terminal window and cds into the current Finder folder with one click.
It's a simple idea, but it's fairly well executed, and unlike a lot of existing, similar plugins, comes with a lot of options. You can either launch the app from the dock, add a buttom to the Finder toolbar, or add an option to Finder's context menu. You can also make it cd into the selected Finder folder instead the selected Finder folder, use the current Terminal window instead of a new one, use a new Terminal tab, or even use iTerm instead of OS X's built-in Terminal. It's certainly not one of those tools that every Mac user needs, but if you spend a lot of time figuring out file paths and using the cd command in Terminal, it can be a pretty sweet time saver.
OpenTerminal is a free download for Mac OS X only.