The 18-55 is a hopeless lens if you want bragging rights on forums less intelligent than this one. No good at all for impressing the ladies on Brighton Pier. But if you want to take pictures with it, it does the job just fine.
For landscapes, it's got a good range of focal lengths, and as you will be using it at around f/8 or f/11 most of the time, it produces results that really are very little different to much more expensive units. Plus, as you will be lugging two cameras around now, the small size and super light weight are a real bonus.
Try to avoid using it wide open, and at the extremes of the focal range: it has nasty barrel distortion at 18mm and isn't great at 55. But don't rush out and replace it until after[/] you have the other lenses you need:
* A wide angle is a must, both for landscapes and for all sorts of other things. The Cannon 10-22 is superb if expensive, and there are several 3rd party lenses in this range that get excellent reports.
* A portrait lens is good to have. Best choice might be the Canon EF-S 60mm macro f/2.8; an excellent portrait and landscape lens, with the added bonus of real macro ability. Alternatively, the 50mm f/1.8 costs practically nothing and works very well. (I have both, although I seldom use the 50 because the 60 macro is so sweet and the slightly longer focal length suits me.)
* You may wish to have something in the medium telephoto class, a 70-200 or a 50-150. I don't use those lengths much, so between the 60 macro and my 100-400, I don't need anything else, but your mileage may vary.
Only after you have covered those other needs is an 18-55 replacement worth considering.
) and cheap as chips.
