Hi everyone. I've been following this thread since I started playing. It has helped me out multiple times and now I would like to share my knowledge with the rest of you. I'm level 19 and have bred and hatched 2 sun dragons and 1 moon. Of all the "tips" posted so far, I think one may have been true. The breeding and incubation times for both are 48 hours and the eggs look like a checkerboard. I bred all three at 2:30 - 3:00 pm EST. time makes no difference in which you will get.
The dragons I used were all level 10.
Blue Fire + Crystal got me my first sun.
Sonic + Storm got me my second sun.
Sonic + Storm also got my my moon.
Feel free to add me and check it out. GC is same as here: Shavemeshavers. If I can post screenshots, I will.