I have the Canon 35mm f/2, 50mm f/1.8 and 85mm f/1.8. Of those, I use the 35mm most, 85mm next, and hardly ever the 50mm due to the handling of the lens. Specifically for close up still life work, I do wish I had a nice 50 to go in there, so I've been thinking about upgrading.
Must be sharp for most of frame (crop sensor) at f/2.8.
Bigger aperture than f/2.8 is nice to have but not essential.
Smooth bokeh quality is of very high importance, more so than roundness. e.g. I'd take a smooth polygon over a harsh circle.
Native higher magnification is a big plus, more than 1:4 is good, 1:2 excellent.
Otherwise should be able to take extension tubes well.
Doesn't need to be AF - therefore any manual lens is a consideration.
Doesn't need infinity focus, as long as it can focus out to a few meters is ok.
Can be prime or zoom. Should at least cover part of range 45mm to 60mm, ideally 50mm.
I've made some rough notes on some lenses below, some that I've owned to give indication of what my expectations are, and some that I've considered. It is by no means comprehensive. I could use suggestions for other manual lenses, Nikon (with aperture ring, no G stuff) and other brands too.
So far I think the Zeiss 50mm f/2 macro is the best quality lens to meet my needs, but I'm not sure it is worth its price. I'd very likely make do with something cheaper if not as good.
Lenses I've used:
Canon 35mm f/2.0 - bokeh could be better, hints of purple fringing on highlights
Canon 50mm f/1.8 - low magnification, focus ring, purple fringing risk
Canon 85mm f/1.8 - low magnification, strong purple fringing
Sony 50mm f/1.4 - low magnification, bokeh could be better
Tamron 28-75 f/2.8 - far too soft at f/2.8
More interesting possibilities:
Zeiss 50mm f/2.0 macro - expensive, MF only
Canon 60mm f/2.8 macro - bokeh could be better
Canon 50mm f/1.2 - expensive, purple fringing risk, low magnification
Canon 50mm f/1.4 - IQ??? low magnification
Canon TS-E 45mm - IQ??? low magnification
Less interesting possibilities:
Sigma 50mm f/1.4 - focus shift alone is deal breaker
Zeiss 50mm f/1.4 - probably not sharp enough, slight focus shift
Canon 50mm f/2.5 macro - probably not sharp enough at f/2.8
Canon 17-55 f/2.8 - low magnification, bokeh could be better
Canon 24-70 f/2.8L - not sure if it's sharp enough at f/2.8
_________________Canon DSLRs: 7D2, 7D1, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 85/1.8, 135/2+SF, 70-300L, 100-400L, 100L, MP-E 65, EF-S 10-18, 15-85
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 50/1.4A, 150 macro, 120-300 f/2.8 OS
Compacts: Sony HX9V, Fuji X100.