On June 7, 2004, David R. and I attempted to see the planet Venus cross in front of the Sun. The attempt was fun, but unsuccessful. It was too cloudy, but even more importantly (and embarrassing for the author), we were looking 24 hours too early – the transit was to occur on June 8; I discovered my mistake, but it rained on the 8th.
I just reviewed the NASA information about it. It is a rare event! The previous time had been in 1882. But the next time is not too far away: 2012 on June 6. Put that on your calendar!
Here are some pictures from our attempt using a popular (but not very high quality) Meade telescope.
Setting up to see transit of Venus across the Sun
Projecting Sun and clouds onto screen (3x5 card)
Mysteries So Bright 
I read some more about the Venus transits. The one in 2012 will be my only chance to see one. Here is a table of these events from the NASA site listed in the post:
Transits of Venus: 1901-2200
Date / GMT / Separation *
2004 Jun 08 / 08:19 / 627″
2012 Jun 06 / 01:28 / 553″
2117 Dec 11 / 02:48 / 724″
2125 Dec 08 / 16:01 / 733″
* distance (arc-seconds) between the centers of the Sun and Venus
And Mercury has more frequent transits, but still rare compared to our lifetimes. Here is a table for Mercury:
Transits of Mercury: 2000-2050
2003 May 07 / 07:52 / 708″
2006 Nov 08 / 21:41 / 423″
2016 May 09 / 14:57 / 319″
2019 Nov 11 / 15:20 / 76″
2032 Nov 13 / 08:54 / 572″
2039 Nov 07 / 08:46 / 822″
2049 May 07 / 14:24 / 512″
Boyd
By: T. Boyd on January 20, 2009
at 3:43 pm