One of the most amazing lenses you can get for your Sony A-mount (or E-mount via adapter) is certainly the 50mm f/1.4 Sigma ART lens. The lens now got reviewed by Kai from Digitalrev (video on top) and by Gordon from Cameralabs who writes:
The new Sigma 50mm f1.4 ART is a truly excellent lens which comfortably out-performs anything costing even twice the price. It sets a new standard for 50mm lenses and easily earns our Highly Recommended award.
The A-mount lens can be preordered in USA Amazon (Click here) at BHphoto (Click here) and Adorama (Click here). And in Europe at WexUK (Click here) and WexDe (Click here).