Nedit it a great tool to create Mel and other scripts. If you don't have it installed, download it from the Nedit website.
This preference file lives in your home directory as .nedit and has syntax highlighting for Mel, RIB, PRMan Shading Language and many other scripting & programming languages.
It also contains some Shell scripts that allow you to source and run your Mel scripts in Maya from within Nedit (no need to type source myProgram; in the Script Editor).
It also contains some Macros that will launch a dialog box containing the help info from Maya on a selected command or simply tells you whether it's a command or MEL script.
To use the Mel source and run scripts, you must have the Maya "mcp" command in your $PATH. On Maya startup, you then run the "commandPort" command. Now from any shell, you can send commands to Maya using the mcp command.