Mmmm, I love my 11-16.... LOVE it

, Overread listed some other good options you have aside from the Canon 10-22. The Tokina if not the most significant upgrade would be a huge one. The build is soo much better than that of the kit lens you currently have, the front element doesnt rotate when you zoom or focus, it has a focus scale which is nice, comes with a petal hood, sharp at all apertures, 5.6 is sharp as hell, which I believe is the sweet spot for this lens, and slowly degrades from there.
Cons for me would be smaller things such as the focus ring acts as the MF->AF "switch" too which you push/pull to toggle between manual and auto.. convenient at times, sometimes not so much. The lens cap comes off quite easy. As a Canon user the zooming is "backwards" hehe. Its also hard to find in stock.
Would you find use for the 2.8 at all? Some people wonder why an UWA would need 2.8, but I think the other way around.. its an ultra wide angle, which will get a ton in focus despite the f/stop used due to the focal length so why not have a wide maximum aperture? If youre interested in a UWA strictly for landscapes perhaps a wider zoom range would be more ideal for you ( not sure ).