Venus and Mercury orbit the Sun inside of Earth's orbit. Since neither planet revolves around the Sun in exactly the same plane as Earth, they usually do not pass directly in front of the Sun. Such a passage, which happens at inferior conjunction, across the Sun's disk is called a transit. It is not an eclipse because they appear only as a black dot on the solar disk.

Venus:
Transits of Venus are rare, taking place at over 100 year intervals and usually in pairs. The last pair of transits of Venus were in 1874 and 1882.
2004 - The first of a current pair was on 8th June 2004 which began early morning, wholly visible from Europe.
2012 - The second of this pair is on June 6th 2012. After that transits of Venus won't occur again until December 11th 2117 and December 8th 2125.

Mercury:
Transits of Mercury are more frequent and take place in May and November.
2003 - The most recent transits of Mercury were in 1993 and 1999 and then in 2003 on 7th May. On the latter date a transit commenced from the upper left-hand side of the Sun at about 7.00h SST, crossing the upper part of the Sun from left to right, and left at about 12.45h SST. At this time Mercury was at such a distance from Earth that it was not visible to the naked eye. It is safe to project the Sun's image by means of a small telescope onto a white card.
2006 - The next transit of Mercury in 2006 is during inferior conjunction on 8th November 2006, with first contact at 19:12 UT and last contact at 0:10 UT. This will be visible from the Pacific Ocean, East Asia, Australia, America and Antartica.
2016/2019 - May 9th 2016 and November 11th 2019.
2032/2039 - November 13th 2032 and November 7th 2039.
2049/2052 - May 7th 2049 and November 9th 2052.