Aside from the different care requirements, habitats, and taxonomic differences, they also do have physical differences.
This is an adult fat-tailed gecko:
http://www.herpcam.com/images/fattail800.jpg
This is an adult leopard gecko:
http://www.lawrencehallofscience.org...opardgecko.jpg
Fat-tailed geckos are brown with darker brown bands. They sometimes have a white stripe down their backs and they have shorter snouts and darker eyes. Leopard geckos are yellow with brown or black spots, lighter eyes with clearly visible vertical pupils. They also come in many other color varieties.