While there are many monsters to choose from since the show has ran (for the past 13 years), below are only a handful of the monsters the Winchesters have faced. Some are the baddest of the bad while others are just super common. You will find descriptions, characteristics, and how to kill each one. Study up - you've got work to do.
Click on the pics for more information on each creature located at McAllen Public Library and other sources.
A blood-drinking race of monster, vampires were once human before being turned. Vampires have strong scent-tracking (once they have your scent, it's for life), they are not hurt by the sun, holy water is nothing but a bath, and stakes through the heart will only upset them.
They can only be killed by decapitation if you can get past their pack and get close enough.
Actual Factual Dracula by 
The Complete Idiot's Guide to Vampires by 
God isn't the only god in town.
The show has seen several gods from various religions coming out to play.
Gods such as Kali (Hindu), Prometheus (Greek), Odin and Baldur (Norse), Mercury and Veritas (Roman) and other lesser known gods and god-like creatures.
They're extremely powerful and extremely temperamental.
Werewolves are dangerous and bloodthirsty creatures ruled by the full moon. They don't spout fur, but they do crave human hearts.
The only way to bring them down? Silver bullet to the heart.
Curse of the Full Moon by 
The Last Werewolf by 
Werewolves by 
Rosemary's Baby
The Conjuring
Cujo
Penny Dreadful
The result of human souls going to Hell and being tortured for centuries on end (time works differently in Hell), demons are dark, malicious, evil spirits that thrive on chaos and death.
How do you kill a demon? Well, you don't. You can exorcize them from the body and send them back to Hell, but this can sometimes kill the host's body. Holywater burns like acid which keeps them in check, but doesn't do anything further than that.
Good luck.
Angels? A villain? How can this be?
Well, angels are a species of supremely powerful celestial beings that serve as God's messenger, attendants, and soldiers. There are a handful of Archangels such as Lucifer, Michael, Gabriel, and Raphael, and other lesser known angels.
As they are so powerful, not every angel views humans as worthy of their father's (God's) love and affection.
With great power, sometimes comes great egomaniacal behavior.
Ghosts are deadly and quite common.
Ways to repel: salt and iron.
Use salt as a barrier and iron as a weapon to dispel the ghost. Those are only temporary fixes, the permanent way is to salt and burn the body of the ghost.