I do Ashtakshara Mantra Japa (108 times, morning) and Gayatri Devi Mantra Japa (108 X 3 times) during Sanyavandana Pooja daily. Mantra is effective when it is received from Guru (Teacher) only.
List of mantras given below is inclusive not exclusive.
Mantra:
The root 'Man' in the word Mantra comes from the first syllable of that word, meaning 'to think', and 'Tra' from 'Trai' meaning 'to protect' or 'free' from the bondage of Samsara or the phenomenal world. By the combination of 'Man' and 'Tra' comes Mantra.
A) Hinduism:
1) Pranava Mantra: AUM
There are Mantras for each deity as Moola Mantra, Gayatri Mantra, Maha Mantra, Bija Mantra, etc.
2) Moola Mantras:
Om Namo Narayanaya (Ashtakshara for Vishnu)
Om Namah Shivaya (Panchakshara for Siva)
Om Saravanabhavaya (Sashtakshara for Kartikeya)
Om Sri Ganapataye Namah
Om Sri Maha-Lakshmyai Namah
Om Sri Durgayai Namah
Om Sri Sarasvatyai Namah
Om Sri Bala-Parameshvaryai Namah
Om Sri Tripura-Sundaryai Namah
Om Namo Bhagavate Vasudevaya
Om Sri Krishnaya Namah
Om Sri Ramaya Namah
Om Sri Hanumate Namah
3) Gayatri Mantras:
Gayatri Devi Mantra:
ॐ भूर्भुवस्वः ।
तत् सवितुर्वरेण्यं ।
भर्गो देवस्य धीमहि ।
धियो यो नः प्रचोदयात् ॥
Om bhur bhuvah svah
Tat savitur varenyam
Bhargo devasya dhimahi
Dhiyo yo nah prachodayat
Durga Gayatri Mantra:
Om Kathyayanaya Vidhmahe
Kanya Kumari cha Dheemahe
Thanno Durgaya Prachodayath
Lakshmi Gayatri Mantra:
Om Mahadevyaicha Vidhmahe
Vishnu Pathniyaicha Dheemahe
Thanno Lakshmi Prachodayath
Saraswathi Gayatri Mantra:
Om Vakdeviyai cha Vidhmahe
Virinji Pathniyai cha Dheemahe
Thanno Vani Prachodayath
Shiva Gayatri:
Om Tat Purushaya Vidhmahe
Mahadevaya Dheemahe
Thanno Rudra Prachodayath
Narayana Gayatri Mantra:
Om Narayanaya Vidhmahe
Vasudevaya Dheemahe
Thanno Vishnu Prachodayath
Rama Gayatri Mantra:
Om Daserathaya Vidhmahe
Sita Vallabhaya Dheemahe
Thanno Rama Prachodayath
Krishna Gayatri Mantra:
Om Govindaya Vidhmahe
Gopi Vallabhaya Dheemahe
Thanno Krishna Prachodayath
Narasimha Gayatri Mantra:
Om Narasimhaya Vidmahe
Vajra Nakhaya Dheemahe
Thanno Narasimha Prachodayath
Ganesha Gayatri Mantra:
Om Lambhodaraya vidmahe
Mahodaraya deemahi
Thanno danthi prachodayath
Subrahamanya Gayatri Mantra:
Om That Purushaya Vidhmahe
Maha Senaya Dheemahe
Thanno Shanmuga Prachodayath
Hanuman Gayatri Mantra:
Om Aanjaneya Vidhmahe
Vayu puthraya Dheemahe
Thanno Hanumath Prachodayath
Aadithya [Sun] Gayatri Mantra:
Om Bhaskaraya Vidhmahe
Diva karaya Dheemahe
Thanno Surya Prachodayath
4) Maha mantras:
Maha-Mrityunjaya Mantra:
Om tryambakam yajamahe
sugandhim pushtivardhanam
uurvarukamiva bandhanaan
mrityor mukshiya maamritaat
Hare Krishna Maha mantra:
Hare Rama Hare Rama
Rama Rama Hare Hare
Hare Krishna Hare Krishna
Krishna Krishna Hare Hare
5) Bija Mantras:
HAUM: 'Om Haum Shivaya Namaha'
In this Mantra, Ha is Siva and au is Sadasiva. The nada and bindu mean that which dispels sorrow. With this Mantra, Lord Siva should be worshipped.
DUM: 'Om Dum Durgayei Namaha'
Here Da means Durga, and u means to protect. Nada means Mother of the universe, and bindu signifies action (worship or prayer). This is the bija Mantra of Durga.
KREEM: 'Om Kreem Kalikayei Namaha'
With this Mantra Kalika should be worshipped. Ka is Kali, ra is Brahman, and ee is Mahamaya. Nada is the Mother of the universe, and bindu is the dispeller of sorrow.
HREEM: 'Om Hreem Mahamayai Namaha'
This is the Mantra of Mahamaya or Bhuvaneshwari. Ha means Siva, ra is prakriti, ee means Mahamaya. Nada is the Mother of the universe, and bindu is the dispeller of sorrow.
SHREEM: 'Om Shreem Mahalakshmiyei Namaha'
This is the Mantra of Maha Lakshmi. Sha is Maha Lakshmi, ra means wealth, ee is satisfaction or contentment. Nada is the manifested Brahman, and bindu is the dispeller of sorrow.
AIM: 'Om Eim Saraswatyei Namaha'
This is the bija Mantra of Saraswati. Ai stands for Saraswati, and bindu is the dispeller of sorrow.
KLEEM: 'Om Kleem Krishnaya Namah'
This is the Kamabija. Ka means Kamadeva, the Lord of desire; it also means Lord Krishna. La means Indra, the ruler of Heaven, also lord of the senses. Ee means contentment or satisfaction. Nada and bindu mean those that bring happiness and sorrow.
HOOM: 'Om Hoom Bhairavaya Namaha'
In this Mantra Ha is Siva, and u is Bhairava. Nada is the Supreme, and bindu means dispeller of sorrow.
GAM: 'Om Gum Ganapatayei Namaha'
This is the Gneasha bija. Ga means Ganesha, and bindu is the dispeller of sorrow.
GLAUM: 'Om Glaum Ganapatayei Namaha'
This is also a Mantra of Ganesha. Ga means Ganesha, la means that which pervades, au means luster or brilliance, and bindu is the dispeller of sorrow.
KSHRAUM: 'Om Kshraum Narasimhaya Namaha'
This is the bija of Narasimha, a very fierce half man half lion incarnation of Lord Vishnu. Ksha is Narasimha, ra is Brahma, au means with teeth pointing upwards, and bindu means dispeller of sorrow.
B) Jainism:
Namokar Mantra.
Namo Arihantânam Namo Siddhânam Namo Âyariyânam Namo Uvajjhâyanam Namo Loe Savva Sahûnam Eso Panch Namokkaro, Savva Pâvappanâsano, Mangalanam Cha Savvesim, Padhamam Havai Mangalam
C) Buddhism
Om wagishwari hum
Om mani padme hum
Om vajrapani hum
om vajrasattva hum
Om ah hum vajra guru padma siddhi hum
Om tare tuttare ture svaha
Om tare tuttare ture mama ayurjnana punye pushting svaha
Om amarani jiwantiye svaha
Om dhrum svaha
Om ami dhewa hri
Om ah ra pa tsa na dhih
Hung vajra phat
Om muni muni maha muniye sakyamuni swaha
Om gate gate paragate parasamgate bodhi svaha
Om maitri maitreya maha karuna ye
Namo bhagavate Bhaishajya-guru vaidurya-praba-rajaya tathagataya arthate samyak-sambuddhaya tadyata OM bhaishajye bhaishajye bhaishajya-samudgate svaha
Om ami dewa hri
D) Sikhism:
The Gurmantra:
"Waheguru"
Moola Mantra:
Punjabi: ੴ ਸਤਿ ਨਾਮੁ ਕਰਤਾ ਪੁਰਖੁ ਨਿਰਭਉ ਨਿਰਵੈਰੁ ਅਕਾਲ ਮੂਰਤਿ ਅਜੂਨੀ ਸੈਭੰ ਗੁਰ ਪ੍ਰਸਾਦਿ ॥
ISO 15919 transliteration: "Ika ōaṅkāra sati nāmu karatā purakhu nirabha'u niravairu akāla mūrati ajūnī saibhaṃ gura prasādi"
Simplified transliteration: "Ik ōaṅkār sat nām kartā purkh nirbha'u nirvair akāl mūrat ajūnī saibhaṃ gur prasād ||"
English: One Universal Creator God, The Name Is Truth, Creative Being Personified, No Fear, No Hatred, Image Of The Timeless One, Beyond Birth, Self-Existent, By Guru's Grace.

