i have a nikor 135. is was much cheaper then the sinaron but after using both 135's for years, i can rarely tell them apart buy looking at negs\scans\prints. nikor is the price preformance.
another really nice option of you are in to the semi wide 135mm is a Fujinon EBC 125mm f5.6.
one of the sharper lenses out there, and is pretty cheap as well. f you get one make sure you get one with the later shutters (usually means a later lens as well). the image circle is as big as it is on the nikor 135mm or bigger (i think its better then 200mm but i am not sure).