Its' G15 Binder is an AddOn designed to improve integration between the Logitech G15 Gaming Keyboard and WoW. It provides simple G-key binding: just point at a button in-game and hit the G key to bind it. You can also display which keyboard mode is active via a border around the active action buttons, or set the mode to control which action bar page is active.
Please note: this AddOn does not create or manage action bars or buttons. There are a plethora of other AddOns out there that do a far better job than I could ever hope to. This AddOn will work with your existing action button set up, be it the default Blizzard bars, or heavily customised Trinity bars. Heck, you could probably bind G18 to the 'Post Auction' button if you really felt like it...
Documentation can be viewed online.
If you want some buttons in the shape of your G keys, give G15 Buttons a try. Please note that I did not write G15 Buttons, nor have I used it; it was merely mentioned by a user.