When I taught the younger grades, I san almost everything. It's fun for the kids and it helps them to learn. Now that I teach 3rd, I don't sing nearly as often, but for some things I do. I have a song for the watercycle, for area/perimeter, and a few others.
Here are some of the songs I've used:
http://www.youtube.com/watch?v=Yw275056JtA (water cycle)
http://www.proteacher.org/a/12048_Water_Cycle_Song.html (water cycle)
http://www.myteacherpages.com/webpages/AmandaCasey/resources.cfm?subpage=1270029 (helping verbs)
http://www.myteacherpages.com/webpages/MonicaM/files/lyrics%20(where%20do%20you%20start%20your%20letters).pdf (letter formation)
There are many others. I will continue posting them as I find them. Check back often!