If you're planning to take the popular June 7th SAT, the regular registration deadline has come and gone, but late registration is available until Wednesday, May 28th. The June exam is popular among high school juniors. Scores will be available online on June 26th. If you aren't happy with your scores, you have all summer to beef up your skills and then retake the exam in October. Register online here. You'll need to pay a $27.50 late registration fee on top of the regular exam fee.
To learn what SAT scores you're likely to need to get into some of the country's more selective colleges and universities, these articles can help: