B&H is having one its periodic one-day price reductions on this excellent lens. [advertiser link]
If you don't have a wide-angle zoom for your DX or EF-S camera and are looking for one, US$100 off (19% off) is a very nice reduction.
The question that always comes up is this: 11-16mm or 11-20mm? Frankly, I've not found a lot to distinguish between the two, so I tend to recommend that you let price help you decide. Today only, the 11-20mm is the lower priced model, so it would be the one I recommend to you.
As for the older models versus the newer atx-i models, I've also not found anything different between them optically. The atx-i models have a slightly more modern build, and perhaps a very slight advantage in water repellence (I don't believe the older models had a water-phobic front element coating).
