I've seen one transit of Venus (June 8, 2004) , and hope to see one more in my lifetime in 2012. If you miss that one, you have to wait until 2117 for the next one.
At other times, it is a spectacular phase.
I've made an animated GIF from 18 images I've been taking during 2004, 2005, 2006 and 2007 of the planet Venus. You can tell how the distance between Venus and the Earth increases and diminishes over time, and how the planet Venus, being an Inner Planet (between us and the Sun), has phases like the moon.
The images were taken through the telescope at http://www.slooh.com/.
To see the animation, click http://www.myslooh.com/data/members/1627/1198986501.gif.
They will be edge on in 2009, and as you can see the rings are beginning to appear smaller than in 2004.
Between these two images of Uranus, I imaged the 5 moons of Uranus known to exist when I began to become interested in astronomy as a child. We now know of 27 moons orbiting Uranus.