The two top ones are fertile, I cant see the one at the bottom properly to tell wether it is also.
but as amosygal said, the top left one has started to develop.
As far as I know, it is impossible to tell if an egg is fertile or not just by looking at it, since all eggs (also unfertile ones) have a tiny white spot.
If you look at the sticky at the top of the "incubating and hatching eggs" in the index, post #4 from the moderators has a good picture of fertile vs. nonfertile including freshly laid. I can pull one from the nesting box and tell.