Venus will transit across the disk of the Sun. This rare event will be visible from many locations around the world. You’ll need glasses/filters suitable for a solar eclipse to keep from burning your eyes out.
The transit will be best viewed from the Pacific Ocean. North America will be able to see the start of the transit (June 5), while South Asia, the Middle East, and most of Europe will catch the end of it. (June 6)
See http://eclipse.gsfc.nasa.gov/transit/venus/city12-1.html to find your local transit times.
Cross your fingers for good weather since the next Venus Transit won’t be until December 2117.