Pop-Up

http://www.sheppardsoftware.com/mathgames/popup/popup_addition.htm 

http://www.sheppardsoftware.com/mathgames/popup/popup_subtraction.htm 

The two games listed above are both excellent sources for actively teaching addition and subtraction to students in a fun and exciting manner. The first game is an addition game and is called Penguin Party. The second game is a subtraction game and is called Pearl Search. These games allow students to gradually enhance their addition and subtraction skills through five different levels of addition facts (e.g., 1-2, 3-4, 5-6, etc.). The games also let students choose their own playing mode (Normal/Easy or Super) which dictates the speed of the games. This along with the ability to choose the different addition/subtraction facts is great since it allows the student to challenge themselves and gradually build up their addition and subtraction skill set.

In my classroom, students would have the ability to play these games as a free time activity before and/or after instructional time. Just like the previous games that have been mentioned, these games could be used during centers.