Some manual focusing f1.2 standard lenses have a nearly mythical reputation because of their ability to dissolve the background and to create a specific "3D look". Mainly the Minolta Rokkor MC 58mm 1:1.2 is highly sought after (CHF/EUR/USD 300 - 600.-- depending on model and condition). Other lenses with a distinctively rougher bokeh (such as the Canon FD 1.2/55mm or the Minolta MD 1.2/50mm) easily gor for 200 - 300.-- CHF/EUR/USD.

Interestingly, the bokeh of theses lenses often is not very good - in fact their forgrund bokeh is much smoother.

If you really want a smooth background, have a look at the MC 1.7/85mm lens (scroll down) ...

Canon FL 1.2/58mm, one of the earliest f1.2 lenses for SLRs: The lens contains radioactive thorium glass on the rear side. It renders quite soft wide open, but it has a bokeh which is one of the best in this test! The lens is also quite sensitive to flare as can be seen in the lower part of the image. 

Canon FL 1.2/55mm - the successor of the above FL 1.2/58mm. It has a better contrast than the FL 1.2/58, but it's background blur is nowhere as pleasing.

Minolta MC 1.2/58mm - it's a legend! Part of a series of fast high performance lenses presented at Photokina 1968, it was immediatly regognized as Minoltas best standard lens of the time. The high-refractive glass has a yellowish tint, but is not radioactive. The bokeh of the MC 1.2/58mm is one the smoothest of all standard lenses tested here (together with Canons FL 1.2/58mm). The Minoltas detail resolution and freedom from CAs is better than the Canon FL 1.2/58mm. The focal length of the MC 1.2/58mm was measured to be 59.5mm (Popular Photography).

Minolta MC-II 1.4/58mm - officially 58mm, but in reality probably closer to 61mm - is often praised as "poor man's MC 1.2/58mm". Its background blur is smoother than that of any vintage 1.2/50mm lens, and even smoother that the bokeh of Canons FD 1.2/55mm. Especially the re-calculated MC-II version is as sharp as the later MC-X 1.4/50mm which has a excellent reputation among Minolta aficionados.

Konica Hexanon AR 1.4/57mm. The Hexanon 1.4/57mm shares the basic desing (only six lenses) with the Minolta MC 1.4/58mm. Like the Minolta, it can be bought for a mere CHF/USD/EUR 50.--, sometimes even for less. The background blur strength is similar to the Minolta MC 1.4/58mm and Topcor 1.4/58mm. It's shape (outward bent) is opposite to the Minolta/Topcon blur (inward bent)!

Topcor RE 1.4/58mm: An early and huge f1.4 lens for the Topcor RE SLR. Unusual for standard lenses, the Topcor RE is a quite asymmetrical design. Asymmetrical designs are more difficult to correct than symmetrical ones, and the reason behind its asymmetry is the small opening of the Exacta bayonet used by Topcon RE SLRs (the front lens of the RE 1.4/58mm has roughly twice the diameter of the back lens!). The background blur is rather smooth due to the relatively long focal length, but the shape of the blur disks themselves is a bit noisy.

Minolta MC 1.7/85mm - a legendary lens as well. Presented first at Photokina 1968, but re-designed before it was introduced in 1971.

Not a standard lens, but included here to give you an idea of how a good bokeh looks like. I've included the MC 1.7/85mm since none (none!!) of the >20 standard lenses tested here has a good bokeh ...

In fact the MC 1.7/85mm has a pretty nice bokeh: No donut-shaped rings around the "blur disks", and a fairly well controlled swirling.