Halley's Comet. Photograph by James Balog in 1986. The return of Halley's Comet in my lifetime was not as spectacular as it was in 1910. I did not see it myself, the weather was overcast for most of the period it could be seen in my part of the world.
Scientists have only searched through a tiny fraction of our galaxy, and with the fast advances in technology, we can expect many more interesting discoveries in the future. But for now, check out the handy infographic below, courtesy of Space.com, displaying all known types of alien worlds.