How can I set up an editor to work with Git on Windows?

Building on Darren's answer, to use Notepad++ you can simply do this (all on one line):

git config --global core.editor "'C:/Program Files/Notepad++/notepad++.exe' -multiInst -notabbar -nosession -noPlugin"

Obviously, the C:/Program Files/Notepad++/notepad++.exe part should be the path to the Notepad++ executable on your system. For example, it might be C:/Program Files (x86)/Notepad++/notepad++.exe.

It works like a charm for me.

Article How to set Notepad++ as the default Git editor for commits instead of Vim explains parameters of the command.