That's a Grey ratsnake Elaphe obsoleta spiloides. Looks like a nice one too.
Here's a link I found when I did a search on Google under the Latin name.
Grey rat snake
Here's a care sheet link also.
rat snake care sheet
You can keep them the same way you'd keep Black, Red (Corn snakes) or Yellow rat snakes. I kept one for about 10 years and he was a great snake- ate about 5 mice at a time and was around 6 foot in length.