The place to start in preparation to take the SAT or ACT is with the information provided for you by the testing agencies. Both have excellent websites with valuable information describing the test, strategies on test taking, practice tests, and more. The organizations also have self-help books available to purchase as well as online tutorials.
SAT websiteACT website
There are many companies offering test preparation classes and tutorials. The website, reviews.com has an excellent resource section that compares the companies and list their strengths and weaknesses in SAT/ACT test preparation. The resource also provides links to each company's website. Floyd County Schools does not endorse this or any other site or the companies reviewed. This is just provided as a resource for parents.
Some of the companies available are Kaplan, The Princeton Review ACT/SAT, PowerScore, Revolution Prep, Testmasters, Set for College, etc.