In reply to Karakoramian:
Thanks very much, I'm glad you like the photos!
The equivalent Canon setup to mine would be something like:
Canon 11-24mm F4 or Canon 14mm 2.8
Canon 24-70 2.8
Canon 70-300
This is hugely expensive though. Also ask yourself if you need an extreme wide angle (most people find them difficult to use as they make everything look tiny - you've got to get right in the face of your subject).
Something like the Nikon 16-35 or Canon 17-40 are great landscape lenses, and are much cheaper and lighter than some of the extreme wide angles. They also takes filters.
I think Mac's covered the 70 - 200 / 300 very well. I also agree with him that I'd look at a 'standard' zoom first. As John says the 24-105 isn't the sharpest but is a lot of lens for the money.
My go to lens is the Nikon 28-300. It's my least sharp lens and isn't a pro lens, but it's just so practical when I'm out and only want to carry one lens.
Lots of food for thought hopefully