I like songs in the classroom, and I love writing silly songs! Here are links to 2 sites, Audacity and MP3 Rocket. Both are free and safe. Audacity is used by amateur music makers to make and record songs. MP3 Rocket is used to convert youtube videos into mp3 format songs. I have found both VERY useful. Both are very easy to use to make basic songs.
For example, I used MP3 Rocket to turn the youtube videos of the "Fast Food Song" (by the Fast Food Rockers) and the instrumental version of "Boom Boom Boom" (by the Venga Boys) into mp3 format songs. Then I used Audacity to cut and paste the songs together and recorded myself. Bada bing bada boom, now I have a silly song about food! I used it for my 6th graders, and we had fun dancing and laughing.
If you are good at writing lyrics (or know someone who is willing to write them for you), you can search youtube for the instrumentals of a popular song, use MP3 Rocket to turn it into mp3 format, then use Audacity to record yourself over the instrumentals.