Squeeze a couple lemons in a glass, and apply some on your hair and go out to the sun. This will bring out some natural golden highlights without looking fake. Don't stay out too long, and wash your hair well after :)
There is product called sun in that you can buy at Walmart or CVS. It's a natural hair lightener. It's works in heat. So you can either blow dry it or sit in the sun. Or you could try lemon juice. But I recommend Sun In.