Love and hate is certainly the first contrast presented. A quote for this comes directly from the opening chorus:
"from forth the loins of these two foes/a pair of star-crossed lovers take their lives"
Juliet also makes reference to love and hate in her speech on the balcony:
"my only love sprung from my only hate"
Romeo remarks on the opening battle by saying:
"here's much to do with hate, but more with love"
To accompany this contrast is the constrast of light and dark. Romeo sees Juliet on the balcony and refers to her as the sun, then contrasts that by making reference to the moon:
"arise, fair sun, and kill the envious moon"
After the dreadful action of Act III, Romeo says to Juliet,
"More light and light, more dark and dark our woes"
Beyond these contrasts are those of good/evil, youth/age, and instinct/intellect.