This very beautiful image was released by the Spitzer team today showing a galaxy merger in Canis Major. I don't know much about the physics of these things, but what's intriguing to me is the fact that the galaxies seem to be merging edge-on. Possibly, this is just an optical illusion—the larger galaxy certainly seems to be face-on to our line of sight, but the smaller one may be tilted in some dimension.
I would think the odds of galaxies merging in the same plane would be pretty small unless there's some gravitational force inclining them that way. Another possible explanation, of course, is that face-on galaxy mergers make nicer pictures.