Here is one that many know by heart.

Psalm 23 is taken from Biblegateway.com

A psalm of David.

 ¹ The LORD is my shepherd, I lack nothing.
 ² He makes me lie down in green pastures,
he leads me beside quiet waters,
 ³ he refreshes my soul.
He guides me along the right paths
   for his name’s sake.
⁴ Even though I walk
   through the darkest valley,
I will fear no evil,
   for you are with me;
your rod and your staff,
   they comfort me.

 ⁵ You prepare a table before me
   in the presence of my enemies.
You anoint my head with oil;
   my cup overflows.
⁶ Surely your goodness and love will follow me
   all the days of my life,
and I will dwell in the house of the LORD
   forever.