If you're not looking to invest too much right on a lens right now, then how about a Jupiter 8 for the time being.
I currently have a number of 50s - in descending order according to the price I paid for them: ZM Planar; Summarit 50 f1.5; LTM Nokton 50 f1.5 (which I re-bought having always regretted selling my first); a collapsible Soviet 50 f3.5; and a Jupiter 8. I use the J8 just as much as any of my more expensive lenses and have never regretted using it.
The Jupiter 8 is a perfectly fine lens - I'd go as far as saying that it's a very good lens - and is capable of producing lovely images. There isn't a single image I've taken with it that has left me thinking that any shortfall in image quality was a result of the lens (as opposed to my photographic 'eye' or technique). No, the build quality patently isn't as good as that of my ZM Planar, Summarit, or Nokton. Then again, it cost me a fraction of the price and I don't plan on using the lens like a hammer, but simply to make pictures - which it does really well.