Dear Iowa tom:
A latitude and longitude grid map does exist for Earth. It includes not only Lat and Longitude lines every 15 degrees, but also includes the Equator, Tropics of Cancer and Capricorn, the Arctic and Antarctic Circles and the Prime Meridian. I developed it for an educational activity I was doing. It is based on a grid map originally developed by Grant Hutchison, one of the forum's foremost contributors.
The grid has not been available as a stand-alone add-on, but had to be gotten by downloading a much larger package of educational add-ons. I have now corrected that. I have just sent the Lat/Long grid to the Motherlode as an add-on. Look for it in the Earth texture map section in a few days (Motherlode takes a few days to update add-ons). If you need it immediately, email me and I will send you the zip file.
Here is a screenshot (click on the picture)
Enjoy
Frank