Math Mammoth : http://www.mathmammoth.com/
We were blessed to be given the chance to try out Math Mammoth. Math Mammoth was created by Maria Miller, who has a master's degree in mathematics with the teacher educational studies, and minors in physics and statistics. After working with homeschooled students she noticed that the books many homeschoolers used were inferior to what she had used growing up or while studying math. Those experiences prompted her to start writing books especially for homeschoolers. She wanted to create a math curriculum that was easy to teach as well as having it affordable. In addition to Math Mammoth, Maria has also created a website called HomeschoolMath.net which is a wonderful math resource for homeschoolers.
Math Mammoth carries 4 different series of math books which are offered in either pdf form or cd-rom. There is Blue Series (organized by topic for grades 1-5), Light Blue Series (complete curriculum for grades 1-5), Green Series (worksheets organized by topic for grades 3-8), and Golden Series (work sheets organized by topic for grades 3-8).
We were graciously given grade 2 light blue series, green series geometry, and 7th grade golden series to review. With the grade 2 math I found it to be very easy to teach and implement. The graphics are simple which is great for kids who get easily distracted by complex graphics (I have a couple kids with ADHD, so this curriculum is great for us!). This series is a complete curriculum, and for the cost you really can't beat it ($14 each or $27 for both A & B). And then add in that it is reusable, it really is a bargain.
I feel the same with the other series that we used. I like that there are no busy graphics, and that the instructions are easy to follow. The difference with these series and the Blue and Light Blue series is that the Green and Golden series are just worksheets. These are for reinforcement, practice or review...these aren't complete curriculums. But the neat thing about these series are that each workbook is broken into topics, with each page focusing on one topic. There are review pages, but for the most part each page concentrates on one concept. Making easy to assign work to the student. The cost for these series are very reasonable too: Geometry Green Series $7ea; Golden Series 7A $8 (includes cost of answer key) 7B $8.50 (includes cost of answer key).