I like things that are free and here is a good one. Math Mammoth is offering the Math Mammoth Percent ebook for free, now through August 18, 2013. The book is designed for middle school students or students performing in math grade levels six through eight.
If you are unfamiliar with Math Mammoth, this is a good time to check them out. They do not sell their math worksheets and curriculum directly, you have to go through one of several vendors, like the Home School Buyers Co-op, to purchase it. All of the products are available for download, some are available in print and CD format.
Click here for the free Math Mammoth Percent ebook.
Hope you find this useful