Roamy here. The primary landing site for the Space Shuttle is, of course, Kennedy Space Center, and the backup (and what was primary for the early years of the program) is Edwards Air Force Base. There are a number of other alternate landing sites that have never been used, but if you listen to the Mission Control calls during launch, the trans-Atlantic abort sites most often mentioned are Zaragoza, Spain and Banjul, Gambia.
What I had forgotten until I saw this article was that we have used a third landing site in White Sands, New Mexico. In 1982, the STS-3 mission had to land at what was then called the Northrup Strip and later renamed White Sands Space Harbor. Edwards AFB couldn’t be used because of flooding. Two trainloads of support equipment were moved quickly to support the landing.
White Sands Space Harbor has been the training ground for Shuttle pilots for 35 years. With the end of the Space Shuttle program, it will be closed in August.