I'd like to add full frame ultra wide to my bag (Nikon mount) got an older 17-35 (only so-so lens) already. Wish the IRIX 11mm was on this list! So I voted accordingly.
Too bad. What you should have done was added the Tokina AT-X 16-28mm f/2.8 Pro FX Lens (for Nikon), and then voted for that--or better yet, skip that damn vote'n BS and buy it! It's only $549 now at B&H and they'll ship it yesterday!
PS: Tamron has a new one out too (similar) and I wouldn't hesitate buy that either (except I already own the Tokina ;- )
The new Sigma 12-24mm F4 DG HSM Art Lens is on my wishlist of lenses to buy....hope more people will give it a look. Cannon Lenses are too rich for my budget, and I get great results from the Sigma Lenses I have.
The Canon 11-24mm would be fantastic. It's probably the next on my wishlist. The 16-35mm f/4L has been wonderfully useful for me. I don't think most folks will benefit from the extra cost/weight of the 16-35mm 2.8. Either crank up the ISO if you're indoors or get a fast/wide prime like the 20mm 2.8 for a few hundred bucks. That lens also serves great as a bring-along wide-angle to throw on when you find the need for a wide shot but when wide angle isn't your primary purpose.
I suggest anyone with an APS-C sensor get the 10-18mm. It's a freaking steal at the price, super sharp, and will show you exactly how often you'll actually be shooting super wide.