Generic blue mods (which slot in any piece of armor) have high values. They're low in level, but for some reason eclipse many of the high end versions you'll encounter. In most instances, generic mods offer higher than 5% increases to armor and weapon damage, ensuring that their value - across all your kit - is potentially huge. The one downside to farming generic mods is that you'll need a low level character (around 16-18) and hit the Dark Zone, or main route mapped below. In each location, simply look up and shoot the air drop/supply crates you'll see hanging. While there's every liklihood that Massive will nerf this, it's worth doing while you can.