What is an example of foreshadowing in Shakespeare's Romeo and Juliet?

In Act 1, scene 4, Romeo's friends attempt to convince him to attend the Capulets' party with them.  He doesn't particularly want to go because he is feeling quite depressed as a result of his unrequited love for Rosaline.  By the end of the scene, however, they've convinced him to go and try to have some fun.  However, he says,

my mind misgives
Some consequence yet hanging in the stars
Shall bitterly begin his fearful date
With this night's revels, and expire the term
Of a despised life closed in my breast
By some vile forfeit of untimely death. 
But he that hath the steerage of my course
Direct my sail.  (1.4.113-120)

In other words, Romeo has a feeling that going to this party will be the beginning of a fateful chain of events that will end with his death.  However, whoever (or whatever) is in charge of his life's path is directing him to the party nonetheless.  Romeo's words foreshadow his eventual tragic death and the fact that the path to it does, indeed, begin tonight, when he meets Juliet Capulet.

Another example of foreshadowing comes when Romeo and Juliet are saying goodbye to one another after their one night together as a married couple.  Juliet says,

O God, I have an ill-divining soul!
Methinks I see thee, now thou are so low,
As one dead in the bottom of a tomb.  (3.5.54-56)

As Romeo climbs down from her window, Juliet feels as though her soul is predicting something terrible: with him below her, she feels as though he seems like a dead person at the bottom of his grave.  This foreshadows the fact that Juliet will never again see Romeo alive.  The next (and last) time she will see him is just after he has poisoned himself in her tomb, believing that she is dead.