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The amazingly good native primes for m43 have almost ruined the alt lens hobby for me.
It's really hard to justify using alternatives to the 12mm f2, the 25mm f1.4, the 45mm f1.8, the 60mm f2.8 macro, and the 75mm f1.8.
On m43, It's still worth using alts that are long and fast (e.g., 135mm f2.8, 180mm f2.8, etc.), have a special look, or just so beautifully constructed that it's a joy to take pictures with them.
Thank goodness we still have Canon, NEX and upcoming FF NEX to enjoy our alt lenses on!
Anyway ... to answer your question ... there are tons of really great alt lenses that work well on m43 in the 35 to 70mm range ... but four inexpensive ones that are easy to find and give great results are the:
Olympus OM 50mm f1.4
Pentax 50mm f1.7 ("Pentax-M" model)
Contax Yashica 50mm f1.7
Canon FD 50mm f1.4