Optical instruments for measurement of precise rapid timing have recently given us the capability of going beyond X-ray variability. Observations of several sources have revealed multi-wavelength variations on a wide range of continuous timescales from ms up, and intriguing flux correlations with X-ray fluctuations have been found. These give unique and quantitative insight on the interplay between various physical components (jet, disc and corona) in inner environments of accreting binary systems. Exciting new developments in this field include measurements of spectral jet breaks between optically-thin and self-absorbed synchrotron emission in several Galactic black hole and neutron star binaries, and detection of strong infrared variability on timescales of seconds to hours. I will review these observations and discuss the new physical constraints on jets and accretion flows emerging from these studies.