I have had to become very familiar with the SAT and ACT in the past year, as we prepared our eldest for college (our homeschooled kid is a freshman psychology major now!). In searching for, first of all, what exactly the tests are and which one is preferred by colleges in our area, I researched study guides and practice tests.
For students who are planning on taking the SAT exam, I found a good free online e-textbook set, which includes free SAT prep as well as free SAT practice tests.
The CK-12 non-profit foundation offers their SAT Prep Flexbooks – free, online, digital e-textbooks with practice tests – through their INeedaPencil.org site. I like their quote, “You can beat the SAT. You can go to college.” It’s true. I promise. You – or your kid – can go to college. And he can even make it through the first two weeks (oh, wait, that’s mine I’m talking about – he’s only been there that long, and I’m still trying to get used to this new idea!).