A good, dull and basic starting point to get oriented is "An Advanced History of India" by Majumdar, Raychaudhari and Datta.

Historigraphy on the subcontinent is generally very weak, so external sources are often the most interesting. I've read, and can recommend:

A record of the buddhistic kingdoms by Fa Hsein (trans. James Legge)

http://www.amazon.com/record-Bud...

The adventures of Ibn Batuta, Ross Dunn

http://www.amazon.com/Adventures...

The Corporation that Changed the world, Nick Robins

http://www.amazon.com/Corporatio...

Periplus of the Eriythrean Sea

http://www.amazon.com/Periplus-E...

Jean-Baptiste Tavernier, Travels in India (long... didn't finish)

http://www.amazon.com/Travels-In...

There is basically plenty of fun material post Alexander's invasion (326 BC).

Before that, you have to rely on literary and philosophical sources.

The early vedic period and the Indus Valley era are mired in huge controversies, and I've read quite a bit around those periods, but basically, don't go there unless you want aggravation.