Hinduism like any other major religion has many sects or denominations.
Vaishnava worship Vishnu and his avatars (especially Rama and Krishna) as the supreme deity. This is the largest Hindu denomination.
- Madhwas - followers of Madhwacharya
- Shree Vaishnavas - followers of Ramanujacharya
- Rudra Vaishnavas - followers of Vallabhacharya
- Nimbarka Vaishnavas
- Gaudiya Vaishnavism - followers of Chaitanya Mahaprabhu
Sects which are Vaishnava, but are not mainstream Vaishnava include:
Saivites are those who primarily worship God Shiva as Supreme God, both Immanent and Transcendent.
Saivism is the oldest sect of Hinduism, embracing at the same time Monism and Dualism. It focuses on yoga, meditation and love for all beings.
God Shiva is both with and without form; He is the Supreme Dancer, Nataraja; He is the linga, without beginning or end.
Shaktas worship Shakti, the divine Mother, in any one, or many of her forms (Kali, Durga, etc.).
Smartas has free rein to choose whichever Hindu deity they wish to worship. It is a liberal and ecclectic sect.
Balinese Hindus follow a sect of Hinduism which once flourished on the nearby island of Java. The formal name for the sect which Balinese Hindus follow is called Agama Hindu Dharma.
Four sects (http://www.hinduism-today.com/archives/2003/10-12/44-49_four_sects.shtml)