Reflex Math
My district has been using reflex math for about 4 years now and the teachers all concur that it is one of the best programs out there that help build fluency for math facts. By the time students are done, they will be fluent in whichever program you assign them, whether it is addition and subtraction or multiplication and division. This program does come with a cost though, but we have found it to be an excellent resource the help build elementary student math fact fluency.
There are multiple games and stations that students can unlock. Ninja Stars, Frog Leap, Picture Math and some of the more common games played.