Depending on your budget and what you intend to use it for (portrait, landscape, all-around long normal), there are plenty of alternatives available.
75f2 Apo Asph: Sharp, Oh so sharp, and good down to 0.7 meters - but mega bucks!
75f1.4 Summilux: A "long" Noctlilux type of lens. Big, finicky (usually requires the camera to be matched to it for consistent result). Out of production so prices are getting up there - probably $1700 and up.
75f2.5 Summarit: Good lens, very nice handling lens too. Sharp at f2.5, though not Summicron Asph sharp. Expensive for a new one, I think around $1500-1700 though I haven't checked prices lately.
Heliar 75f2.5: small, compact and actually very good. Wide open it has slight softness - typical of the Heliar design. Not unsharp, just a softer look. Good travel lens as it will comfortably fit in a pocket. It is a screw-mount lens so you need to add an adapter. Usually can be had for $300 + adapter. Not a bad lens to start with if you want to try out 75 as a second lens.
Heliar 75f1.8: Brand new lens - available later this month. I have a pre-production sample and I am quite impressed with it. Similar quality wide open as the Heliar 75f2.5 - but slightly sharper even @ 1.8. Bigger than the 75f2.5 - but I find it very comfortable to work with.
Odd ones: Canon's 85/1.5 and 1.9 - older designs and they are probably best suited for portraits. Lower contrast than the modern lenses - which is not all bad, as it can give a unique color rendition - and makes bl/w more pleasing.
Nikkor 85f2 in LTM: Really good lens, slightly soft contrast at f2 (great portrait lens) - chrome ones are HEAVY (as is the Canon lenses!). The black, lighter version, is more expensive - almost on par with the Heliar 75f1.8.
Plenty of choices - enjoy the process.
In cases like this, always check on Flickr for what these lenses can do. Not perfect as the files are small, but it does give you an idea as to color and things like flare/contrast etc.
