Found mostly in India and Nepal, Hinduism is a religion and way of life for over one billion people, making it the third-largest religion in the world. 
Hinduism is largely thought of as the oldest of the world's religions, and it does not point to any single founder or prophet, but rather a diverse spread of Indian cultures and traditions. The synthesis of these roots began to develop from 500 BC and 300 CE.
Hinduism is broad, with a wide range of philosophies and concepts linking recognizable rituals, texts, pilgrimages, and other religious and philosophical pinnings.
The major scriptures in Hinduism are the Vedas and the Upanishads, the Bhagavad Gita, and the Agamas.
Hindus subscribe to 4 Purusarthas, or aims of a human life:
- Dharma: Ethics and duties. A "right" way of living according to the order of life and the Universe.
- Artha: Work, purpose, and goal. This is the means of life, a proper living, financial security, and economic prosperity.
- Kama: Emotions and sexuality. Considered essential and healthy to pursue without sacrificing the other 3 pillars, Kama is want, desire, passion, wish.
- Moksha: Liberation and freedom. Can be understood as a mental transformation of freedom from ignorance and into divine insight. Ultimate clarity and peace.
These compare very interestingly with our Bliss Map.
There are some primary deities in Hinduism, but they are largely considered lower manifestations of an ultimate or supreme reality. Some of these deities are Vishnu, Shiva, Devi, Ganesha, and Surya. Each represents a modern current or way of Hinduism, in addition to Smartism, which is the worship of all 5 deities.
Hindus believe in the existence of the soul, reincarnation of the soul, karma, and dharma (a concrete morality or "right" way of living.) 
Some of the eternal duties prescribed in Hinduism are honesty, refraining from injuring living beings, patience, forbearance, self-restraint, compassion, respect, and acceptance.
Hinduism is different from a traditional Western understanding of religion, as it is very tolerant to variations in belief. There is no unified belief system or creed or declaration of faith. Some think of Hinduism as an umbrella term referring to the religious pluralities of India.
Hindu Website: Exactly what it sounds like. :) A site with articles and essays explaining Hinduism, as well as Buddhism, Sikhism and more.
What is Hinduism: A page similar to this one, but in more detail, explaining Hinduism and providing external links to other resources.
Hinduism.about.com: A fun scroll through of hinduism for beginners. Includes some quick-read articles about Hinduism.
Hindu Universe: International Hindu news on an old-school website.
Hinduism Today: A well-constructed quarterly with Hinduism resources and articles about Hinduism in the world.
Devi: the Great Goddess: an online Smithsonian gallery about the goddess Devi! Cool.
Hindu Online: "World's largest portal on the Hindu religion"
Krishna.com: the leading hinduism blog
BBC on Hinduism: Another good overview page of Hinduism by the BBC.
Our World quick Hinduism: About the shortest video intro to Hinduism you can find. ~2 minutes
Mystic India: a 43-minute video that, while acted and not a documentary, is well-narrated and full of iconic views into India, its aesthetics, myths, and stories. Great for a relaxed, pleasing-to-the-eye look into India.
The History of Hindu India: a really educational documentary split into 3 parts (~20 minutes each). Developed by the editors of Hinduism Today magazine.
God, Soul, and World: Another ~30 minute bottom-up explanation and contextualization of Hinduism by Hinduism Today editors.
Invitation to World Literature: The Bhagavad Gita: a fun half-hour interpretation and contextualization of the most important modern sacred script of Hinduism by various experts.
Sita Sings the Blues: a full film based on the Hindu epic The Ramayana. Incredible animation and the whole thing is set to 1920's jazz vocals. Wow. ~1hr 20min
PBS on Modern Hinduism: a news story about a modern family's use of modern Hinduism. ~8 minutes
Schooltube Hinduism Beliefs and History: a 6-minute overlook with interviews.
Bhagavad Gita Lectures: a one-week series of lectures recorded, explaining the Bhagavad Gita. There are also many other videos on this site.