Ok i'm having a spark of creativity and need something to write down music notes on, however I'm all out of music paper. Is there some kind of program or software that will let me write music on the computer?

http://www.anvilstudio.com/ is freeware, although I never tried it myself. I use http://www.cakewalk.com/products/SONAR/X1-Essential/ but it cost money.

Thanks!