Good suggestion Ramona.
Mercury's synodic cycles are of course significant. I do present the Mercury-Earth cycles in the various Lunar Planners in which they occur (listed on the planetary synodic cycles page), however I do not a have page dedicated to Mercury. I will keep it in mind when I have some extra time. For those unfamiliar with synodic cycles, you can learn more here: Synodic Cycles and Planetary Retrogrades
Mercury-Earth synodic cycles and corresponding retrogrades average 116 days. They are not always of the same duration because Mercury's orbit is highly eccentric, which also effects changes in Mercury's orbital velocity, thus the time it takes for Earth and Mercury to align during their orbits around the Sun varies.The pattern produced is complex as well because of Mercury's eccentricity and elliptical orbit.
Mercury's next transit (across the face of the Sun) occurs in May of 2016.
A full list of transits and more technical information about Mercury's transits can be found here:http://eclipse.gsfc.nasa.gov/transit/catalog/MercuryCatalog.html