There's a new wide angle lens for full frame Nikon, Canon and Sony/Minolta DSLRs. It's the Tamron 15-30mm f/2.8 Di VC. Note this lens is designed for full frame DSLRs, it's an effective 21-36mm Focal Length on APS-C sensor cameras.
Matt Granger thinks that in many areas (not all) it rivals the Nikon 14-24mm f/2.8. Click here to get Matt's review. If this is true, it's pretty earth-shaking! For a very long time, the Nikon 14-24mm has been considered the very best wide angle lens there is.
The Tamron is $790 less than the Nikon 14-24mm and is available for Canon and Sony/Minolta in addition to Nikon. If it's as good as Matt says it is this may be a new best in class for real estate photography.
Also, it's worth noting that I don't see a Adobe Lightroom profile for this lens but that shouldn't last long, I expect there will be one within a month or two.
Update Feb 7, 2015: Thanks to Mark who pointed out in the comments below that Canon also announced a 11-24 f/4 . I'm remiss for not noticing this. This new ultra-wide lens is due to be released later this month. The price will be around $3,000 USD. This piece of glass truly deserves the UFWA designation!