I personally like the addon "G15 Buttons (continued). It lets you specify keybinds, so rather than setting up macros in the G15 editor, you can assign keystrokes like you do in the wow keybinds. Really helps for modifer macros, etc. It comes with a GUI of the G15 keys, so you can drag your spells to the key you want to use.

There are detailed instructions on how to set this addon up @ the following link: http://www.curse.com/downloads/details/9562/

Also, if you are using Vista, read this thread for the solution to a potential problem with vista and the G15 profile app.

Issue with G15 Keys Addon.

If you decide to go this route, let me know if you have any issues and I will try my best to help you.