Collins Electro-Optics I3 intensified eyepiece; 25 mm; new $1995 10/2000; used 6 times; warranty remaining; I will sell for $1500.
It's cool - increases visual by 2 magnitude, without averted vision. Lights-up galaxies, nebulae, clusters. See it in Sky and Telescope and on their web site: http://www.ceoptics.com/index.html
My experience with this eyepiece is very favorable. I purchased it because I wanted to easily increase the "aperture" of my scope on the cheap, and this is one way to do that. It intensifies light very good, making observing much more interesting. Globular clusters and galaxies light up nicely, with direct vision, not averted vision. Photography is another interesting avenue with it, with good pics reported w/ conventional digital cameras in only 8 seconds of exposure. If someone has some money to spend, I think it makes a small scope (i.e., 8-12") at least twice as interesting to play with. Alot cheaper than buying a 20-inch scope! I took it to a star
party recently, and everyone in the host club was wowed by it, and had never looked thru one before. Even on a full moon night, we were able to pick up a some galaxies for demonstration.