What does Satan look like? Many people have seen the Classical depiction of Satan in paintings and statues, but what does scripture say about what Satan looks like?
Apparently, anything he likes, including an angel:

2 Corinthians 11:14:


  ... Satan himself masquerades as an angel of light.


Assuming Satan is an angel, then he can probably take on any appearance, at least that of a human:


  Do not forget to entertain strangers, for by so doing some people have entertained angels without knowing it.


Hebrews 13:2

And possibly a snake (though some Christians do not take this passage literally)


  Now the serpent was more crafty than any of the wild animals the LORD God had made.


Genesis 3:1

More information can be found on the Christian demonology Wikipedia article.