I was reading this book: Sourcebook in Indian Philosophy by Sarvepalli Radhakrishnan and Charles Moore.

These are my notes:

Indian philosophy is one of the longest continuous developing system of philosophical thought. They gave importance to the philosophical system than the people behind them.

Four major periods of development:

Sruti Period (Vedic Period):

from 2500BC to 600BC. All of the vedas: Rig Veda(hymns, philosophical), Sama Veda(melodies), Yajur Veda(sacrifical formulas), and atharva(spells and incantations for long life, health, etc), were written in this period. All of the Vedas were divided into four parts: Samhita(mantras), Brahmanas, Aranyakas, and Upanishads. Samhita (Mantras) were hymns written by the poets. Brahmanas were written by the priests and were the religious rituals. Aranyakas were about meditations in the forest, where old people going to the forests tried to replace their social rituals. Upanishads, were philosophical texts which talked about the results of meditations. Upanishads started talking about spiritual monism which is a characteristic of much of Indian philosophy. Intuition rather than reason started taking importance.

Smrti Period (Epic Period):

from 600BC to 200AD. Most of the philosophical development took places in this time. Mahabharata (incl the Bhagavad Gita), Ramayana were written this time. most philosophies were founded in thought. heterodox philosophies like jainism, and buddhism were also formed. Mostly spontaneous insights and constructive imagination.

Sutra from 200AD to <unknown>. Here the philosophies developed in the earlier period was systematically written into short sutras (aphorisms). Systematic Orthodox Hindu systems were writtten (as sutras). Self-conscious thought and reflections. The sutras were very concise. Six orthodox systems were written: Nyaya (logical realism), Vaisesika (realistic pluralism), Samkya (evolutionary dualism), Yoga (disciplined meditation), Purva Mimamsa (earlier interpretative investigations of the Vedas), Uttar Mimamsa (later investiations of Veda, also called Vedanta Sutra, or Brahma Sutra).

Scholastic Period:

from end of Sutra period to 1700AD. Here the philospher wrote commentaries on the Sutras, and commentaries on those commentaries. These are explanatary and polemical to other systems. One famous example: Samkara's commentary on Vedanta.

Rig Veda's Hymns:

1017 in 10 books. Starts from polytheistic, and goes to monotheistic and monism. Compiled in present form around 1500BC, though it is believed that they were "composed" earlier than that, and only "compiled" at around 1500BC.

The hymns do various things. They:

1. Treat qualities of natural phenomena as Gods. Praise them. Maybe this praising nature later resulted into the praising/thanking nature of the Indian people?
2. Talk about one God, from which everything has risen. (monotheism, monism)
3. Talk about a universal law (called Rta, which is Ra?), a universal unity, and the rule which the whole natural world follows.
4. Talk about moral conduct -- they tell that people should do good, like help other people, not tell lies, not cheat the husbands (for girls), not to deceive people, believe in charity, be honest, not be theives, etc.
5. Talk about doubts, doubts about the existence of Gods

There is a mention of the caste system, dividing the people into four castes: Brahmin(priests), Rajanya (warriors; another name for Kshatriya), Vaishya (agriculturists, traders), and Sudra ( the servile class). There is a mention of the marriage system, since they say that "wives should not cheat". There is a mention of Heaven (ruled by Visnu) and Hell (ruled by Yama), where good and bad people go, respectively.

Some of the hymns show marked intelligent thought. The following are some example hymns:

• Hymn of Creation (Book 10, Hymn 129), belonging to type (b) above: (Taken from the book linked at the top of the page; that book in turn sources it from "The Hymns from the Rigveda" by A.A. Macdonell (Oxford Univ Press, 1922) )

  Non-being then existed not nor being:
  There was no air, nor sky that is beyond it.
  What was concealed? Wherein? In whose protection?
  And was there deep unfathomable water?
  
  Death then existed not nor life immortal;
  Of neither night nor day was any token.
  By its inherent force the One breathed windless:
  No other thing than that beyond existed.
  
  Darkness there was at first by darkness hidden;
  Without distinctive marks, this all was water.
  That which, becoming, by the void was covered,
  That One by force of heat came into being.
  
  Desire entered the One in the beginning:
  It was the earliest seed, of thought the product. 
  The sages searching in their hearts with wisdom, 
  Found out the bond of being in non-being.
  
  Their ray extended light across the darkness:
  But was the One above or was it under?
  Creative force was there, and fertile power:
  Below was energy, above was impulse.
  
  Who knows for certain? Who shall here declare it?
  Whence was it born, and whence came this creation?
  The gods were born after this world's creation:
  Then who can konw from whence it has arisen?
  
  None knoweth whence creation has arisen;
  And whether he has or has not produced it:
  He who surveys it in the highest heaven,
  He only knows, or haply he may know not.
  

• Book 8, Hymn 89. [type (e)]

  Striving for strength bring forth a laud to Indra, a truthful hymn if he in truth existeth.
  One and another say, There is no Indra. Who hath beheld him? Whom then shall we honour?
  

• Book 2, Hymn 12. [type (e)]

  Of whom, the terrible, they ask, "Where is he?",
  Of whom, indeed, they also say, "He is not."
  The foemen's wealth, like player's stakes, he lessens, 
  Believe in him: for he, O men, is Indra.
  

• Antiquity and Continuity of Indian History by Prasad Gokhale: This gives a interesting, detailed description of Indian history ... though it ends up with dates which are in complete contrast with usually accepted dates (western) of the Indian History. I saw some other articles as well, regarding the dates of Indian history, which all give different dates; all of which make me sure of the fact that we, are NOT CERTAIN, of the dates of Indian History. It is a sad thing. Now I have started beleiving that the Aryan Invasion Theory is certainly false, and that Vedic Civilization was actually much older than that. The above link is a local copy of the article -- taken from this webpage.
• On the Chronological Framework for Indian Culture(PDF) by Subhash Kak (he has an extensive history page) : this is another long, interesting, and eclectic article on trying to come up with Indian history chronology
• Myth of Aryan Invasion
• The Demise of Aryan Invasion/Race Theory