Actually... These three books from Math Mammoth Blue Series aren't technically freebies, but they have been set to "Pay What You Want" at Currclick, which means you choose how much you pay.
You CAN get them for free if you cannot afford to pay :)
Math Mammoth Place Value 2 (for grade 2)
Math Mammoth Add & Subtract 4 (for grades 4-5)
Math Mammoth Percent (for grades 6-7)
They allow you to get a good overview of my products -- for free!