Originally Posted by Addy101
But apparently the Sony 10-18/4 is quite good and it is cheaper then the Sigma 8-16 if you have to count in an adapter (however, if you also use a DSLR, I would go Sigma).
Samyang also has some newer and interesting ultra wide options made for mirrorless:
12mm f/2 (available):
10mm f/2.8 (upcoming):
There are photo samples in those links as well.