Paul's Online Math Notes
If you google "math notes," this site is usually listed first on the google search engine. This is one of the most popular math reference sites internationally; it was created and is maintained by an outstanding professor at Lamar University (I've taken three classes from him myself). These detailed sets of notes and examples range from Algebra (College Algebra) to Differential Equations. So, many of your Pre-Cal and/or Calculus reference needs can be met with a visit to this site. Just click the link and scroll down until you see "Class Notes and Tutorials". Also, there are some quick facts in the "Cheat Sheet and Tables" section. Check it out!