I wanted a Gmail icon for my desktop that just showed whether I had mail or not, and the number of new messages. Although there are a few geeklets already that achieve this, none of them behaved exactly the way I wanted so I created my own.
The script retrieves your Gmail password from Keychain, but unlike some of the others, I have hard coded the username (just update this in the script) since I have multiple accounts saved in keychain and I needed it to pull the correct one.
The notification badge I originally had as another separate image geeklet that I changed the visibility for at runtime, but the layering kept messing up as a result and often the badge would end up covering the number in the z-order. As a result I just embellished the actual mail icon png instead which still works and means one less geeklet too.
To install, just update your Gmail username in the script and make sure the two image files are in the right spot (I have them in the folder "Gmail_Geeklet" in my Documents folder... just update the script if you want them somewhere else). I did notice that when I had them in a folder which contained a space, the images didn't work, hence the underscore.
Hope this is useful.
