There are 18 "sheep dog" breeds recognized by the AKC:

Australian shepherd
Australian cattledog
Bearded Collie
Collie
Border Collie
Cardigan Welsh Corgi
Pembroke Welsh Corgi
German Shepherd
Old English Sheepdog
Briard
Shetland Sheepdog
Bouvier Des Flandres
Puli
Belgian Tervuran
Belgian Malinois
Belgian Laekenois
Belgian Sheepdog
Canaan Dog