Flocabulary is a hip hop/rap website focusing on vocabulary in the classroom. I pick out my Flocabularies (yes, I made up that word) for the week and the kiddos are thrilled. They ask for them and are thoroughly disappointed when they haven't made one for the topic we are covering that week. The money rap is by far our favorite! They had it memorized and belted it out every morning when we started math during those lessons. The non-fiction text features one is also pretty awesome. I typically use the Flocabularies at the beginning of each lesson so that they review what we talked about. They would much rather sing along than even talk to their neighbor about our topic.
We used the multiplication raps in order for 1-2 weeks for each set of facts. This really helped the kiddos memorize their facts. Check out this one on YouTube. Don't worry, Flocabulary doesn't actually run through YouTube. They just have a YouTube channel for you to check out some of their raps for free.
The price is a little much...$96/year, but it's worth it! Not only do they have the raps for topics, but they also have a set of vocabulary words for each grade level with a rap for every 5-10 words. Then, they include worksheets, quizzes, study guides, the lyrics, etc. to go with each rap.
Check out the the free month long trial and then make your decision.