Characteristics

• Are humans that have been transformed by another vampire
• Transformation occurs when a human ingests vampire blood
• Have a second set of sharp retractable teeth that extend beyond their regular teeth
• Enhanced senses
• Enhanced strength
• Sleep during the day
• Nest in groups of roughly 8-10
• Mate for life
• Can live off animal blood rather than human
• Not repelled by crosses, garlic, sunlight or stakes to the heart
• Can easily pass for human

Vulnerabilities

There are only two ways of killing a vampire:

• Beheading
• The Colt

Although Dead Man's Blood can be used as it acts like a posion to them. The most useful method of using the blood is via a crossbow bolt.

Groups

Luther's Group
Living in Manning, Colorado, Luther was the undisputed leader of the pack, closely followed by his mate, Kate. A very traditional pack of vampires, they capture humans, taking them back to their lair to feed on. Most of the group, including Luther and Kate were killed by the Winchesters.
As seen in episode 1x20 - Dead Man's Blood

Lenore's Group
In Red Lodge, Montana, this group lived very differently to Luther's. They live off cattle, not humans. It's not something they enjoy, but they do it for survival. Even when Sam's blood is dripped into Lenore's face, she managed to control her hunger enough to retract her fangs. Despite being hunted by Gordon Walker, most of the group survived and moved somewhere new. They have a tentative agreement with the Winchesters.
As seen in episode 2x03 - Bloodlust

Dixon
When the rest of Dixon's group was killed, he started building a new "family". Using vampire blood and posing as a drug dealer, he approached young girls in nightclubs, tricking them into trying the blood. Although not seen for definite, it is probable that Dixon was killed by the Winchesters.
As seen in episode 3x07 - Fresh Blood