One of those terms that you have to be careful mentioning unless you enjoy getting mired down in pseudo-New Age discussions about mysterious cosmic forces. The Great Attractor was discovered in 1986 by group of astronomers calling themselves The Seven Samurai, led by Alan Dressler, who noticed that the velocities of near-by galactic clusters appeared to have a perpendicular component superposed upon the Hubble flow. In other words, the universe is expanding, but most of the near-by galaxies are being pulled towards relatively small point in space. In fact, whole Virgo Cluster (ours) and most of the Hydra-Centaurus supercluster were being pulled in the direction of Centaurus. Closer examination indicated that said point was both a) really freaking massive, on the order of 5*10^16 solar masses, or about 100,000 galaxies worth of stars, making it one of the heaviest known "single" objects in existence, and b) squarely located behind the disc of the Milky Way, meaning that whenever we point our telescopes at it, we don't see anything except, well, the Milky Way.

The unfortunate combination of the Attractor's enormous magnitude and low observablility, along with some mumblings about dark matter meant that the initial announcement was met with a great deal of skepticism, and for a while, the whole concept failed to gain wide acceptance, despite ten years of meticulous data collection and analysis.

In recent years, however, dedicated study of the galactic plane on the radio and x-ray bands, which penetrate the dust and gas of the Milky Way, indicate that there is indeed an enormous galactic cluster about 250 million light-years away in the direction of the constellation Norma (the Level; I guess they ran out of good constellation names in the southern hemisphere). This cluster is believed the be the bright, shining center of the largest, most massive supercluster known, and it's just incidentally in about the same spot as the "mythical" Attractor was supposed to be. No one has said anything official yet, but there are an awful lot of papers with tiles like "Really Huge Cluster of Galaxies in Great Attractor Region," and the correlation between the two is pretty widely accepted.

If you are looking for pictures, the official name is ACO (Abell) 3627, but it's really not very impressive. Only the brightest and most active galaxies are even visible through the dust, and even those look muted.
For more information and a good look at modern astronomy in general, check out Alan Dressler's Voyage to the Great Attractor