You can engrave on pretty much everything, except for PVC hard metals without any coating. Stone, yes. pillows, yes. ipods, yes. tshirts, yes. acrylic, yes. wood, yes.
PVC's a no because it yellows and can ruin the laser, hard metals just don't take a dent.
Everything else, you can engrave, or just cut straight through. Ah, the wonders of vectoring and rastering!