C'Tan. It's a brilliant read, especially if you're a bit in the dark about Necron lore. Its also pretty damn funny in places!
The second is on The Void Dragon. Now I'm not going to give to much away, I'll leave it to the man himself, but another fascinating read. Spoilers from the Horus Heresy novel Mechanicum inside. This is a really thought provoking article about the whole 40k universe. Brilliant stuff.
So head on over and give these two a read.