The Nikon 135mm F/2 DC is really a hybrid of the Canon 135mm F/2.8 SF and the stellar EF 135mm F/2L, which is a pretty stellar combination. The 135L does have a few advantages in terms of sharpness and resistance to CA. My favorite "bokeh monster" is the absolutely insane Minolta (now Sony) 135mm F/2.8 (T 4.5) STF. A lens with such a cult following it has its own domain name. It's manual focus, and manual aperture. Wide open it has the DoF of F/2.8, but the light transmission of F/4.5. The light loss is due to a "apodization" element that is a concave dish facing the objective (front) element. The lens has more or less mathematically perfect (gaussian) bokeh circles. As one might expect, it's exceedingly rare and rather expensive (though not any more than the Nikon 135mm DC.)
DigitalRev TV previously covered the 105DC. It's pretty fascinating viewing if one is a bokeh-obsessed photo nerd.