Any alt UWA for ff?
Zeiss 18mm and 21mm - the latter is supposed to be good.
Samyang 14mm - cheap, sharp and fast. Manual focus only, bulbous front element and complex distortion.
Tokina 16-28 has been getting some rave reviews. Has bulbous front element (i.e. no filters).
Tokina 17-35 is new but is rather good (from the first reports anyway)
Sigma 12-24 is very wide but has bulbous front element (no filters) and is not the sharpest lens. Almost no distortion, however. There is a version II which is sharper but with more distortion.