Tokina 11-16mm 2.8, useful for your landscape photography too.
User gp link
http://www.clubsnap.com/forums/sigma-tamron-tokina/776104-tokina-11-16mm-f-2-8-user-group.html
User gp link
http://www.clubsnap.com/forums/sigma-tamron-tokina/776104-tokina-11-16mm-f-2-8-user-group.html