In my quest to paint all of my unpainted miniatures, the next obvious choice is another squad of Warp Spiders. When I've used them in games, they've been one of my favorite units. Adding another full squad couldn't hurt.
I went for a darker scheme to differentiate this squad from my original squad. The method I used for painting the red was taking from my recent Menoth models. I really like how they came out, with the spider runes providing a bright contrast. Amusingly, I initially planned to paint the Venom spider icon on their backs.
It turns out that it is absurdly difficult to paint those legs and have them come out looking symmetrical. After a few very disappointing attempts, I went with the Warp Spiders' Eldar Rune. I don't think it's quite as striking but the execution is much better.
My next project will be the rest of the squad, another 5 Warp Spiders with no Exarch.