Path Length Checker is a stand-alone app that allows you to specify a root directory, and it gives you back a list of all paths (i.e. files and directories) in that root directory and their lengths. It includes features such as pattern matching and min/max length constraints, as well as the ability to specify a string that should replace the root directory in the results brought back, allowing you to quickly see path lengths if you were to move the files/folders to another location.
Download it from the Releases page.
To run the Path Length Checker using the GUI, run the PathLengthCheckerGUI.exe.
Once the app is open, simply provide the Root Directory you want it to search and press the large Get Path Lengths... button.
The PathLengthChecker.exe is the command-line alternative to the GUI. Simply run it without any parameters to see what parameters you can pass to it.
There is currently a bug with the Path Length Checker tool where it is not able to process paths in Windows restricted directories (e.g. C:\Documents and Settings). In the meantime you can use this PowerShell script to get those path lengths.