I am very happy shooting my Panasonic 7-14mm f/4 (14-28mm equivalent in ff). Olympus just brought out their f/2.8 version a few weeks ago. Olympus also has a 9-18mm though it is slower. I think there's also a couple of primes from Voiglander, Kowa and Samyang that are primes in the "ultra wide" range. Olympus also makes a 12mm prime and I think I've seen maybe a 10mm.
The primes are out there if you search, but I can tell you my 7-14mm is one fine lens!