Thoughts on rare snakes...

http://www.dnr.state.md.us/wildlife/snakeinfo.asp
This is maryland's understanding of their snake distribution. Divided into common, uncommon, rare, endangered, and historical.
The eastern kingsnake is common...

Common
Black Rat Snake (Elaphe obsoleta obsoleta)
Eastern Garter Snake (Thamnophis sirtalis sirtalis)
Eastern Hognose Snake (Heterodon platyrhinos)
Eastern Kingsnake (Lampropeltis getula getula)
Eastern Milk Snake (Lampropeltis triangulum triangulum)
Eastern Ribbon Snake (Thamnophis sauritus sauritus)
Eastern Worm Snake (Carphophis amoenus amoenus)
Northern Black Racer (Coluber constrictor constrictor)
Northern Brown Snake (Storeria dekayi dekayi)
Northern Copperhead (Agkistrodon contortrix mokasen)
Northern Ringneck Snake (Diadophis punctatus edwardsi)
Northern Water Snake (Nerodia sipedon sipedon)
Rough Green Snake (Opheodrys aestivus)
Smooth Green Snake (Opheodrys vernalis vernalis)
Southern Ringneck Snake (Diadophis punctatus punctatus)

Uncommon
Coastal Plain Milk Snake (Lampropeltis triangulum elapsoides X triangulum)
Corn Snake (Elaphe guttata guttata)
Mole Kingsnake (Lampropeltis calligaster rhombomaculata)
Northern Red Belly Snake (Storeria occipitomaculata occipitomaculata)
Queen Snake (Regina septemvittata)
Smooth Earth Snake (Virginia valeriae valeriae)
Southern Copperhead (Agkistrodon contortrix contortrix)
Timber Rattlesnake (Crotalus horridus horridus)

Rare
Northern Scarlet Snake (cemophora coccinea copei)
Redbelly Water Snake (Nerodia erythrogaster erythrogaster)

Endangered
Mountain Earth Snake (Virginia valeriae pulchra)
Rainbow Snake (Farancia erytrogramma erytrogramma)

Historical
Northern Pine Snake (Pituophis melanoleucus melanoleucus)