(The National Day of Prayer may be a semi-blasphemous joke, but I do take prayer seriously. Here are three classics.)
A prayer of St. Francis of Assisi
O Lord, make me an instrument of thy peace.
Where there is hatred, let me sow love.
Where there is injury, pardon.
Where there is discord, harmony.
Where there is doubt, faith.
Where there is despair, hope.
Where there is darkness, light.
Where there is sorrow, joy.
Oh Divine Master, grant that I may not
so much seek to be consoled as to console;
to be understood as to understand;
to be loved as to love;
for it is in giving that we receive;
it is in pardoning that we are pardoned;
and it is in dying that we are born to Eternal Life.
And whenever you pray, do not be like the hypocrites; for they love to stand and pray in the synagogues and at the street corners, so that they may be seen by others. Truly I tell you, they have received their reward. But whenever you pray, go into your room and shut the door and pray to your Father who is in secret; and your Father who sees in secret will reward you.
When you are praying, do not heap up empty phrases as the Gentiles do; for they think they will be heard because of their many words. Do not be like them, for your Father knows what you need before you ask him.
Pray then in this way:
"Our Father in heaven, hallowed by your name. Your kingdom come. Your will be done, on earth as it is in heaven. Give us this day our daily bread. And forgive us our debts, as we also have forgiven our debtors. And do not bring us to the time of trial, but rescue us from the evil one."
And my favorite prayer, from Mark 9:24
I believe; help my unbelief!