I am planning on going around Switzerland for a week to travel through the alps and photograph scenery and landscapes. I also want to rent a lens that would be best for landscape photography. I have a 60D with an 18-55mm, a 28mm 2.8, a 50mm 1.8 and a 70-200 f/4 L. Here are the lenses I am considering to rent:
Canon 10-22mm (I had a Tamron 10-24 when I used to shoot Nikon and absolutely loved the wide angle)
I'm not sure many people actually read your post, since people are suggesting buying lenses, etc.
Since you are renting, get the 10-22. If you were buying, it might be a different set of circumstances, but, renting you should get what works best for your camera. While the 17-40 and 16-35 would be upgrades over your 18-55, they don't really add to what you have. The 10-22 adds a whole different world of shots (10-17mm), which is critical for landscape stuff. And its a rental, so it has no impact on what future lenses you own.
Honestly, with the 10-22, the 28 and the 50, you probably don't even need to take the kit lens. And I agree with others, rent a CPL as well, just be careful when you include the sky in shots. I did my travel this past summer with an ultra-wide, a 28mm, and my 70-200 f/4L, and that is all you really need.