Connect Sums and Sums Stacker are two fabulous sites by Carstens Studios Inc. for practicing addition facts! (Be sure to notice that on the right side of the page, both sites have options for changing from dice to numbers or even to coins. )
Connect Sums is a game where you click on a series of values that adds up to the target sum. The next value clicked in a series must be a neighbor or the last value clicked.
In Sums Stacker the goal is to click and drag values from stack to stack until the sums of each stack equal the target sums below.