Naag has always been given highest positive importance in our Vaidik belief. Naag or serpent has always been a symbol for efficient consciousness. The serpent power in sleeping state symbolizes unconsciousness in man.
If the Naag had not been there the following were not possible --

Naag References in Early Times
(1) Where would Naaraayan float in water without the serpent - Shesh Naag?

(2) How Lord Shiv would look without his snake ornaments?

(3) Where Lord Krishn would have danced if Kaaliya Naag hood was not there?

(4) Kaalee is also adorned with serpents.

(5) Snakes, Kadroo's sons, covered Uchchaishravaa horse's tail and because of them its tail looked black. Vinataa lost the bet and became the maid of her sister Kadroo. Later her son Garud got her freed after giving Amrit to Kadroo.

(6) If this enmity between Garud and snakes, because of the above reason, did not develop, what would Garud eat?

(7) It was only a dead snake, Pareekshit put in the neck of Shameek Rishi, that created such a havoc, that Shameek Rishi's son had to curse the King to be bitten by Takshak on the 7th day from that day.
--If Takshak were not there who would bit Pareekshit, and how he would have died
--and if Takshak had not bitten Pareekshit, Janamejaya would not have done Snake sacrifice;
--and if Janamejaya did not do Sarp Yagya why Vaasuki Naag would have worried about his race, and looked for a way to save it?
--and it was only Vaasuki Naag who saved Naag race from Janamejaya's snake sacrifice by marrying his sister Jaratkaaru to Jaratkaaru. They had a son named Aasteek who stopped Janamejaya's Sarp Yagya.
[see also below No 19 under Naag References in MBH]

(8) Churning of the ocean (Saagar Manthan) was made possible using only Vaasuki Naag.
--all Devtaa and Raahu are alive today only because of drinking Amrit (nectar) which was possible due to churning of the ocean with Vaasuki Naag

(9) All Devtaa and Raahu are alive today only because of drinking Amrit (nectar) which was possible only due to churning of the ocean with the help of Vaasuki Naag.

(10) Takshak Naag stole the beautiful earrings of the queen of the King Pushya from Uttank who was taking them to give to his Guru Maataa as his Guru Dakshinaa. This theft led him to instigate Janamejaya to annihilate the Naag and he organized the Sarp Yagya.

(11) It was Karkotak Naag who stung King Nal to bring about his release from Kali Yug. Note that the Kaurav share many names with the Naag such as Dhritraashtra, Kauravya etc. (see the Garud-Naag chapters).

(12) The ancestor of the Chandra dynasty, King Nahush, was cursed to be turned into a python who held Bheem immobile and Yudhishthir freed him after answering his questions.

(13) Later there is Sumukh Naag who was rescued by Maatali's daughter Gunaakeshee from Garud who must have a meal of a Naag a day (like the Raakshas Bakaasur whom Bheem killed in Ekchakraa Nagaree).

(14) It is believed that when Kundalinee is awakened, the serpent power is awakened. This Kundalinee sleeps in a coil form, 3 and 1/2 times. The 3 coils represent the 3 Maatraa of Om, which relate to past, present and future; to the 3 Gun: Tamas, Rajas and Sattwa; to the 3 states of consciousness: waking, sleeping and dreaming; and to the 3 types of experience: subjective experience, sensual experience and absence of experience. The 1/2 coil represents the state of transcendence, where there is neither waking, sleeping nor dreaming. So, the 3 1/2 coils signify the total experience of the universe and the experience of transcendence.

Naag References in MBH
(15) It is also an epilogue of the epic as Pareekshit's assassination was the revenge for the genocide of Naag in Khaandav Van by Arjun and Krishn. And when Uttank tells Janamejaya of this, it becomes the occasion for another genocidal campaign against Naag (Janamejaya's Sarp Yagya) and the setting for the narration of the epic.

(16) Then there is the dimension of relationships : Kuntee's father's maternal grandfather is the Naag Aaryak whose people save Bheem when he is poisoned and gift him with superhuman strength.

(17) Uloopee, also a Naag maiden, daughter of Naag Raaj Kauravya, loves Arjun, marries him, and has a son from him. Later she resurrects Arjun when he is slain by their son.

(18) In MBH war, Takshak's son Ashwasen came to take revenge of his mother's killing by Arjun. When Arjun offered Khaandav Van many Sarp were living there. Takshak's wife and son were also living there. Takshak's son was able to escape the fire, but his mother was burnt in that fire. When he heard that a war was going on between Kaurav and Paandav, he thought this a good opportunity to take revenge from Arjun, so he went to Duryodhan and asked his permission to fight with Arjun. He hid himself in Karn's arrow which was aimed at Arjun.
(MBH, G-6-War/35)

(19) It was only a dead snake, Pareekshit put in the neck of Shameek Rishi, that created such a havoc.
--If Takshak Naag had not been here who would bite Pareekshit and how would he have died?
--And if Takshak Naag had not bitten Pareekshit why Janamejaya's Sarp Yagya took place to burn Takshak Naag?
--And if Janamejaya did not do Sarp Yagya why Vaasuki Naag would have worried about his race, looked for a way to save it?
--and it was only Vaasuki Naag who saved Naag race from Janamejaya's snake sacrifice by marrying his sister Jaratkaaru to Jaratkaaru. They had a son named Aasteek who stopped Janamejaya's Sarp Yagya.

(20) Janamejaya's Sarp Yagya is famous. He did Sarp Yagya because Takshak killed his father.

Naag References Elsewhere-Naag Festival
(21) In North India, especially in UP, there is a specific day on which Naag are worshipped. This day, known as Naag Panchamee, falls on Krishn Panchamee of Shraavan month of India Lunar calendar. This Vrat (fast) and festival has been described in Agni Puraan, 20, also.

(22) Egyptian sculptures and painting are full of snake references.
http://www.google.ca/search?q=king+pharaoh+with+snake&start=10&hl=en&sa=N&qscrl=1&nord=1&rlz=1T4ADFA_enCA440CA448&prmd=imvns&tbm= isch&tbo=u&source=univ&ei=MP7qT87u JrKM6QGprZTtBQ&ved=0CFQQsAQ4Cg&biw=1022&bih=437
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The following two books with reference to Naag are with DLI - please check up their usability:
1. Indian Serpent-Lore or the Nagas in Hindu Legend And Art / by J Ph. Vogel , PhD
2. Tribes in Ancient India... Law / by Bimala Churn, Natural Sciences. English, 1943. 462 p.