If you just finished a pre-algebra text, the obvious next step is an Algebra I text. The usual sequence in high school is Algebra I, then geometry, and then pre-calculus, which is a combination of Algebra II, trigonometry, and analytic geometry. Once you're through all that, you're ready for calculus, which is necessary to truly understand most serious scientific subjects.
Note that this sequence takes three years for most students, and if you can only study part time, it may take longer, so don't be discouraged. Keep plugging away, because there are no short cuts. You MUST be competent in algebra and trig before you take calculus. And geometry teaches you not just facts about triangles and circles, but how to think and reason mathematically.
As for books, I suggest you save your money and get them from the internet. These subjects have been around for so long that the differences between texts is more style than substance, so just try to find one that seems to be at the right level and pace for YOU. Many very generous professors have written texts that you can download from their websites - just google for them. Here's a decent algebra text:
http://tutorial.math.lamar.edu/Classes/Alg/Alg.aspx
You can look at each section online, or download a complete PDF from the "downloads" section.
Also, there are thousands of old texts that are out of copyright, and available for download from Google. Go here:
http://books.google.com/advanced_book_search
and check the button that says "full view only," and then search on algebra or geometry or whatever. You will find many textbooks that were written 100 or more years ago, but are still perfectly usable. In fact, some of the modern texts are so full of fluff trying to "make math fun" that they are hard for me to read.
Download a few and try to find one with an agreeable writing style for you. Don't make the mistake I often do and waste days or weeks searching for the "perfect" text. Good enough is good enough.
Also, whatever text you use, be aware that in every math class I've ever taken, we never read every chapter and section, and we never do all the problems in a given section. Especially with modern books, there are many more problems in the book than any teacher would assign. It's important to do *some* problems, but if you did every problem, it would take a week for each section. If you do end up with a modern textbook, you may want to google on its title and "site:.edu" to find colleges that use it, and look for a course syllabus that tells what problems are assigned by that teacher.
Good luck to you.