What are really good online prep websites and prep books that will really raise my score on the SAT?

http://blog.prepscholar.com/how-to-get-a-perfect-sat-score-by-a-2400-sat-scorer

At the top end of the scoring range, the SAT is not forgiving. You need to aim for perfection.

Specifically, here's what you need to do in each section:
•in Reading, you can only miss 1 or 2 questions. This depends on the curve for that test. It's best to aim for missing 0 or 1 question. In my test, I missed 1 reading passage question.
•in Math, you need to get every question correct. No question about it. The curve is unforgiving for Math. Miss 1 question and you won't get an 800 on this section.
•in Writing, you can sometimes miss 1 question at most. In some tests, you have to get a perfect Writing and Language score to have a shot at an 800.

Essentially, you need to aim for perfection during your prep. If you're consistently missing 1 or more questions on each section, you're not performing consistently enough to be safe for a 1600. We'll go into more detail about this below.
You need the motivation to push yourself. You need to put SAT prep as one of your top priorities in life, overcoming watching Youtube or hanging out at the mall.

In the darkest of days, when you take a practice test and drop 100 points inexplicably, and your parents are freaking out, and you're worried you're never getting into your top college, you need the inner fire to not get depressed. Instead, you need to pull yourself up and objectively rip apart your mistakes so you don't repeat them.

People don't often mention motivation, but in my view this is one of the most important pieces that differentiate successful people from not, in all aspects of life. It's much more important than just being smart.

Make a list of all the reasons you want to get a perfect score. Write them down. Stare at them when you lose faith.
On the ground level, when you're actually studying, this is by far the most important way you'll succeed over other students.

EVERY mistake you make on a test happens for a reason. If you don't understand EXACTLY why you missed that question, you will make that mistake over and over again.

If you're performing at the 700 level, you're missing around 10% to 15% of all questions. This means you have some consistent errors that are holding back your score.

This is what you need to do:
•on every practice test or question set that you take, mark EVERY question that you're even 20% unsure about
•when you grade your test or quiz, review every single question that you marked, and every incorrect question. This way even if you guessed a question correctly, you'll make sure to review it.
•in a notebook, write down the gist of the question, why you missed it, and what you'll do to avoid that mistake in the future. Have separate sections by subject and sub-topic (reading - passages vs sentence completion, writing - sentence errors vs improving paragraphs)

It's NOT enough to just think about it and move on. It's NOT enough to just read the answer explanation.

You have to think HARD about why you specifically failed on this question.

By taking this structured approach to your mistakes, you'll now have a running log of every question you missed, and your reflection on why.

Everyone who wants to get to an 800 on a section has different weaknesses from you. It's important that you discover for yourself what those are.