Leica R
To this day a lot of this glass is hard to beat. My Summilux-R 1.4/50 still is the best fast 50 I have used for an SLR and I've owned many from Zeiss, Nikon, Canon etc. The 50 Lux and Summicron-R 2/50 are the two reasons why I still shot with R bodies.
Other notables include the Summicron-R 2/50, Macro 2.8/60, Summilux-R 1.4/80, Summicron-R ASPH 2/90, APO 2.8/100mm. These are really, really good lenses and just like with the M glass, I do see a noticeable difference in scans and wet prints, between the R glass and the Zeiss and Nikkors I shoot.
The Summilux-R 1.4/35 is underrated, as is the last version of the Summicron-R 2/35. The ultra wides get very good reviews (19mm ? etc). A lot of the long Leica R glass is truly outstanding, as are the 2.8/35-70, 4/35-70, 28-90, 4/80-200, 2.8/80-200.
But as with everything Leica, their pricing placed them totally out of the mainstream. I think the 2.8/80-200 went for $6000 in the early 2000's.
Zeiss Contax
I never owned a Contax, but two of my friends did and the results were impressive. But I now have the 2/35 Distagon, Planar 1.4/50 and 1.4/85 in Nikon F mount and as expected these are really good lenses.
Canon FD
Canon made some very impressive glass in the old FD mount. Erwin Puts speaks very highly of this line up. Lot's of impressive high speed 50's and I think Canon was one of the first companies to start to use ASPH surfaces.
Nikon
I'm also a Nikon guy, but I always felt that their lens lineup was somewhat uneven. You have real standouts like the 2/28, 2/50, 1.4/50 AIS, Micro-Nikkor 3.5 (2.8) /55, 1.4/85mm, 2.5/105. But then there are lenses like the 2/35, which to be polite, is really weak. The 1.4/35 also never impressed me. Really soft at 1.4. There are some really cool f1.2 fifties. Not the sharpest, but they render really beautifully.
I always thought that Nikon made the best SLR bodies around, but for some reason they would keep a lens in their line up for 20 years and never update it, while the rest of the industry did.
Early on I also shot a little Pentax and really liked their fast 50's. Maybe not the sharpest lenses, but my god did they draw beautifully in b/w. Mike Johnston waxes about this lens on occasion. It's like the SLR version of the Leica M Summicron-DR 2/50.