One of the best ways to develop fluency with basic number facts is through games. When we play, we have fun. Enjoyment causes chemical reactions in our brains that make it easier for information to stick. We are having fun AND learning at the same time.
The games you find here are not websites for individual practice. Rather, they are social games that require at least 2 people to play. Social interaction while learning is critical in mathematics. As we talk about the strategies we might be using or what we are seeing, our brains are making connections. This makes our learning stick.
The National Council of Teachers of Mathematics has a great link to ILLUMINATIONS. Illuminations is full of games, online manipulatives, and teaching ideas.