In planetary physics, the Lagrange points are points in a two-body system where the gravitational attraction from the two bodies are equal. There are five such points; L1-L3 are unstable while L4 and L5 are stable. The Earth-Moon L4 and L5 points have attracted interest as possible sites for space colonies.
But what's already there? There has only been one space mission through L4 and L5 (the Hiten spacecraft), which found no increase in the amount of interplanetary dust. (That was the only instrument it had.) It seems to me that all sorts of interplanetary flotsam should end up there, from dust to fairly good-sized rocks. Some of them should be visible (via light or radar) from the ground. It would also seem to be a good place to collect samples of interplanetary flotsam; much easier than going all the way out to the asteroid belt.