Found this little flash gem, and am addicted.
(For some reason, I am having more fun with this than I was with FL Studio...I hope some of you know what that is.)
You can right click and select copy/paste a code of the grid, so should you come up with a really cool melody, feel free to share :P
Here are a couple:
86672,256,512,49216,512,2304,16912,0,49160,512,8320,16900,2048,8,94240,576
36996,32,512,32776,34880,0,33284,0,36994,0,544,32772,8456,0,33312,512
73872,2048,74240,2056,8704,2048,8196,2048,41224,2048,8192,34896,8192,0,43072,0
EDIT: forgot the link, thanks Chip :P
http://lab.andre-michelle.com/tonematrix