I picked up a 20 dollar copy of the Battle of Macragge a little while ago. I converted some of the marines into Chaos Marines and then my eye fell on the Nids. I put some models together and painted them, and it was a real joy! I loved the lines, the different levels of depth and the nastiness of the expression.
Here are the ones I did:
Here's the boss from behind:
It was really fun to paint these models and I am kind of looking to build a small, 1000 point army of them, just to set a goal to do some interesting paintwork.