Jean Meeus writing in the December 2002 Sky & Telescope predicted an occultation of Ganymede by Europa for 23:25 - 23:37 UT on February 3rd 2003. Sure enough, as I watched through the cloudless skies of Shepherds Bush, the slightly dimmer (redder?) blob of Europa approached Ganymede, merged, and came out on the other side. He also predicted an eclipse of Ganymede by Europa for 23:35 - 23:45, but I couldn't detect this, probably because it was over by the time I could resolve the two moons again. The occultation and eclipse were so close in time because Jupiter was at oppostion on February 2nd.
