5 Dice (Free)
Roll the dice and try to come up with a problem that hits the target answer, using 5 dices and all the operations. Great for teaching order of operations! Connect with a second player via bluetooth to compete against one another.
Math Party Free (Free Version) This free version allows for two people to play on one device. Play by tapping on bubbles with totals from smallest to largest, kids as young as age 5 can play at the lowest levels. The free version gives number order, roman numerals, the alphabet, and multiplication. The full version ($0.99) allows for 4 levels of difficulty, with each player choosing its level.
Mathfeud (Free) Complete the number sentences, in a layout similar to Boggle. The more you complete, the more points you get. Compete for points through levels with other players via Mathfeud. This requires an account set up in order to search online for other students.
My favorite is the app to play with my kids is Numbler ($1.99) I found it when it was free, but I still think it would be worth the $1.99. Think of scrabble with numbers! It allows you to play alone against the computer or with another player on the same device. The most recent update also connects to the Game Center to play with players that are on other devices.
Anyone have any other math apps that they like to use?