Various order-disorder phenomena have been studied from microscopic observations of μm-sized polystyrene particles in magnetic fluids (ferrofluids). The basis for this is that the holes created by the particles in a magnetized fluid appear to possess magnetic moments antiparallel to an external field. The effective dipolar interactions between the particles (holes) may be made attractive or repulsive and varied relative to the thermal energy due to Brownian motion. Various many-body effects are visualized including formation of triangular, chain, and lamellar structures of spheres. Nonspherical and magnetic particles are shown to form structures with competing interactions. The results are interpreted qualitatively and compared with existing model calculations.