The shortest psalm in Scripture is Psalm 116(117). It is a great one to commit to heart. I find that I need to pray it often, as life can be quite a challenge more often than not.
I am usually praying in Italian nowadays. It is such a beautiful language, so poetic and lends itself well to prayer and psalmody. So here is the psalm in Italian.
Lodate il Signore, populi tutti, voi tutte, nazioni, dategli gloria; perche forte é il suo amore per noi e la fedeltá del Signore dura in eterno.
In English:
Praise the Lord all you peoples! All of you, nations, give him glory. For strong is his love for us and the fidelity of the Lord endures eternally.
When times get tough, when all seems lost, when you seem defeated and all alone, pray with all your heart Psalm 166(117). God is so close to us that he literally permeates our being. He never abandons us. He loves us eternally. Hold his hand and be at rest with him.