Matt, if most of your shots are going to be Landscape, then I'd go for either the Canon EF-S 10-22mm f3.5-4.5 USM or Tokina 12-24 F4 DX. You can never have too wide a lens for landscape work. The Tokina will be a lot cheaper than the Canon but is comparable optically, the 10-22 being that little bit wider. If you can fit them in, it would also be worth taking a tripod and some filters (particularly ND and polarising). Here is
review by Bob Atkins of the Tokina with reference to the Canon 10-22 as a comparison.