Some post-Vedic texts, including the Mahabharata, the Natyasastra and certain Puranas, refer to themselves as the “fifth Veda”. The earliest reference to such a “fifth Veda” is found in the Chandogya Upanishad.

“Divya Prabandha”, for example Tiruvaymoli, is a term for canonical Tamil texts considered as Vernacular Veda by some South Indian Hindus.

Other texts such as the Bhagavad Gita or the Vedanta Sutras are considered shruti or “Vedic” by some Hindu denominations but not universally within Hinduism. The Bhakti movement, and Gaudiya Vaishnavism in particular extended the term veda to include the Sanskrit Epics and Vaishnavite devotional texts such as the Pancaratra.

source: http://en.wikipedia.org/wiki/Vedas