The Math Game Time website has free and simple math games for students between pre-kindergarten and seventh grade. The Manga High website has a variety of math games for every grade and offers free access to full games for those who sign up.
Multiplication.com is a site centered on teaching and memorizing the multiplication tables and features games that accompany math problems. The games on the Hooda Math website are well-produced and cover the three broad categories of logic, arithmetic and geometry. There are several games in each category with varying degrees of difficulty.
Illuminations is an educational site without advertisements that emphasizes learning. The games on this site are intended more for exercise than play. However, there are many games to choose from that cover not only elementary math but advanced topics for high school math and beyond. There is a home page where you can select each game based on a specific skill that is taught while you play it.
Arcademic Skill Builders offers an online resource of games for addition, subtraction, multiplication, fractions, integers and decimals. There are also games that deal with money and time. These games are geared toward elementary and junior high level math.