Before practice, we always take refuge in the three jewels: our teachers, the teachings, and those others who travel along the path of awakening with us. these supports are traditionally referred to as Buddha, Dharma and Sangha.
You can find a good discussion about refuge along with half a dozen traditional prayers at Unfettered Mind.
Traditional Tibetan Refuge Prayer
This prayer was written by Atisha, a famous Indian teacher of the 11th century who emigrated to Tibet.
Until I reach enlightenment, I take refuge in all the Buddhas
And in the Dharma and all the noble Sangha.
By the merit of accomplishing the six perfections
May I achieve buddhahood for the benefit of all sentient beings.
Modern English Refuge Prayer
This was written by Jetsun Yeshe (Catherine Rathbun), a lay teacher of Buddhism who teaches in Toronto. Printed with permission.
The Mind of Light is called Enlightenment
In this I take Refuge
The Body of Truth is called the Dharma
In this I find solace
The Teachers of Truth are called the Sangha
In them I find comfort and courage.
My mind is not separate from the Mind of Enlightenment
I vow to sweep away its cobwebs
My knowledge can grow to be an exhibition of Truth
I vow to burnish my awareness
My body is a storehouse for learning and development
I vow to treat it with honour and kindness.
The energy of breath rising is the energy of growth
The energy of breath falling is the energy of return
The midpoint of balance is the place of union
Where Body, Speech and Mind join together
and the jump to Transcendent Wisdom
In all these I take Refuge.