The main sources I have used for the history of ancient and medieval India are:
Thapar, R., The Penguin History of Early India, Penguin, 2002, is a full and scholarly overview of the subject, from origins up to 1300 AD, for the general reader.
Keay, J., A History of India, Harper Collins, 2000, is an accessible introduction to Indian history.
Auboyer, J., Daily Life in Ancient India, Phoenix, 1965, is a highly readable look at life in ancient and early medieval India from 200 BC to 700 AD.
Schmidt, K.J., An Atlas and Survey of South Asian History, Sharpe, 1995, provides a clear map-based approach to Indian history, invaluable for the Western reader who is unclear on Indian geography.
A lavishly illustrated work on archaeology for the general reader which includes good coverage of ancient India and the roots of Indian civilization, is Renfrew, C. (ed.), Past Worlds: The Times Atlas of Archaeology, Times Books, 1995, p. 88-9; 130-1; 188-9.
A work on general archaeology aimed more at students, but readable and with very good coverage of ancient India, is Scarre, C. (ed.), The Human Past, Thames & Hudson, 2005, p. 518ff.
The British Museum’s beautiful series on ancient civilizations includes their website Ancient India.
Wikipedia has its usual vast amount of information on the History of India
The Ancient History Encyclopedia has a good section on the Indus Valley – Ancient India – but is a bit sketchy on the rest of ancient Indian history.