No mantras other than any well constructed affirmation. Basically, the best thing to do is:

a) Focus on feeling good. b) Frequently imagining yourself as a great intellectual i.e. imagine the experience of receiving compliments from others about your intelligence, receiving awards and accolades and so on. When imagining try to enjoy it as much as you can. It's nice to do this when you drift of to sleep or are just waking up.

here is the definition of mantras:

"Mantra" (Sanskrit मंत्र) means a sacred utterance, numinous sound, or a syllable, word, phonemes, or group of words believed by some to have psychological and spiritual power.[2][3] Mantra may or may not be syntactic or have literal meaning; the spiritual value of mantra comes when it is audible, visible, or present in thought.[2][4]

Earliest mantras were composed in Vedic times by Hindus in India, and those are at least 3000 years old.[5] Mantras are now found in various schools of Hinduism, Buddhism, Jainism and Sikhism.[3][6] Similar hymns, chants, compositions and concepts are found in Zoroastrianism,7] Taoism, Christianity and elsewhere.[2]

The use, structure, function, importance and types of mantras vary according to the school and philosophy of Hinduism and of Buddhism. Mantras serve a central role in the tantric school of Hinduism.[5][8] In this school, mantras are considered equivalent to deities, a sacred formula and deeply personal ritual, and considered to be effective only after initiation. However, in other schools of Hinduism, Buddhism, Jainism or Sikhism, this is not so.[7][9]

Mantras come in many forms, including ṛc (verses from Rigveda for example) and sāman (musical chants from the Sāmaveda for example).[2][5] They are typically melodic, mathematically structured meters, resonant with numinous qualities. At its simplest, the word ॐ (Aum, Om) serves as a mantra. In more sophisticated forms, they are melodic phrases with spiritual interpretations such as human longing for truth, reality, light, immortality, peace, love, knowledge and action.[2][9] In other forms, they are literally meaningless, yet musically uplifting and spiritually meaningful.[5]

http://en.wikipedia.org/wiki/Mantra

Word have power when they are in truth and make no inequity, also they hold spiritual truth if one is seeking. and since you have ask.

seek and you will find after all is it not written: Ask and it will be given to you; seek and you will find; knock and the door will be opened to you.

http://biblehub.com/matthew/7-7.htm

Make every effort to enter through the narrow door, because many, I tell you, will try to enter and will not be able to.

Luke 13:24-28

http://biblehub.com/luke/13-24.htm

If you are looking for some in English try the bible or the gospel of Thomas.

for truth, reality, light, immortality, peace, love, knowledge and action.

here is a mantras for you:

Look to the living one as long as you live, otherwise you might die and then try to see the living one, and you will be unable to see."

Two will recline on a couch; one will die, one will live."

For this reason I say, if one is whole, one will be filled with light, but if one is divided, one will be filled with darkness."

There is light within a person of light, and it shines on the whole world. If it does not shine, it is dark."

http://www.gnosis.org/naghamm/gosthom.html

If I have been your helper so be it and let it be.

Let there be light , be the light that you can be, experience and enjoy.