9 principal avatars of Vishnu

Following is an overview of the 9 principal avatars of Vishnu :

First incarnation of Vishnu :
Matsya or the Fish incarnation : in this form Vishnu saved the Saint Vaivaswata, the hindu variety of the biblical Noah (or vice versa).

Second incarnation of Vishnu :
Kurma or the Turtle incarnation : at the Churning of the Ocean, Vishnu as Koorma (or Kurma) offered his back as a pivot on which to rest the Mount Mandara, used as a churning stick by gods and demons.

Third incarnation of Vishnu :
Varaha or the Boar incarnation of Vishnu : he killed the demon Hiranyaksha, recovered the stolen Veda's and released the Earth from the bottom of the ocean.

Fourth incarnation of Vishnu :
Narasingha or the Lion incarnation : as a creature who was half-lion and half-man, Vishnu killed the demon Hiranyashasipu, brother of Niranyaksha, who had gained the boon of immunity from attacks by man, beast or god.

Fifth incarnation of Vishnu :
Vamana or the Dwarf incarnation : he killed the demon Bali, who had gained dominion over the Earth and had chased the gods from the heavens.

Sixth incarnation of Vishnu :
Parasurama : he killed the King Kartavirya, who had stolen the holy cow Kamadhenu, which could grant all desires.

Seventh incarnation of Vishnu :
Ram : he killed the demon King Ravana, who had abducted Sita.

Eigth incarnation of Vishnu :
Krishna : he killed Kansa, son of a demon and the tyrannical King of Mathura.

Ninth incarnation of Vishnu :
Buddha : Vishnu incarnated to remove suffering from the world.

Tenth Incarnation of Vishnu :
Kalki : still to come at the end of the Kaliyuga or the present age of decline, when Vishnu will appear in person on Earth, seated on a white horse, Kalki, which is his tenth incarnation.

by http://www.sanatansociety.org/hindu_gods_and_goddesses/vishnu.htm