As you can see from my profile the widest lens I have is 24mm. Although for 90% of the time this is perfect for me, there are times I'd like a wider lens.
I'm quite temped by the 17-40 as it would double up as a nice travel lens.
But I'm interested in some left field suggestions. Maybe some old converted zeiss?
I once owned a Tokina 17mm F4 which I really liked but it had to go back as it caused the camera to error. But these are so hard to find.
Any other alternate suggestions?