I can't afford the (very good) Fujinon 10-24mm zoom at the moment, and I really like wide angle, so to tide me over I thought I'd go for something a little different and try a Fisheye - if you're in a similar situation, this might be a good compromise.
This is the best price I can find without going for a grey import/ebay etc.
The lens uses a type of stereographic projection, which means there's less of a centre bulge and less compression round the edges whilst preserving the relationship of angles in the image.
This makes it pretty good for defishing using programs like Hugin, which gives results roughly equivalent to around 12mm, I think.
As it is, I quite like the plain fisheye effect!
It's a manual lens and build quality is excellent. Also, with this focal length it's very easy to get things in focus.
Here's a snap I took last wednesday with my X-A1 - http://38.media.tumblr.com/a68d22d7b76fb891741b96c57fce75c6/tumblr_n7h3frApwE1s8n7yco2_1280.jpg