Well, The Almost and Skillet are both Christian, so you're good there. (Though I'm sure other kind forum members will have delightful suggestions for further artists to check out.)
Unfortunately, System of a Down is fairly unique in the music world. I've heard several decent clones, but none of the Christian. (If you're curious, hit me up via PM... I don't feel like breaching the "sacred" boundary between the Christian and Secular music forums.)
The closest Christian band would be
Tantrum of the Muse--who embodies (or, more appropriately "embodied" since they've been defunct for nearly 10 years) a similar loud, brash musical backing and off-kilter, hard-to-describe vocal method. That said, the two bands use their similarities to completely different effect.
They might also have the least sanitized lyrics to have ever been found in the Christian market, tackling the darker, deep issues that can challenge and confuse a Christian teenager or young adult. In the black-and-white world of Youth Pastors (sweeping generalization alert!) Tantrum of the Muse would have fallen into the black.
Anyway, if that has sparked your interest, the good news is that the band has put both their full-length albums on the internet for free download:
Unteachers