Dao
No longer a newbie, moving up!
Since you mentioned you looking for landscape photography, you may want to also look at lens that has a smaller number on the focal length. (small mm value = shorter focal length)
such as...
Canon EF-S 10mm - 22mm f/3.5-4.5 USM Autofocus Zoom Len
Tokina AF 11-16mm f/2.8 AT-X Pro DX
such as...
Canon EF-S 10mm - 22mm f/3.5-4.5 USM Autofocus Zoom Len
Tokina AF 11-16mm f/2.8 AT-X Pro DX