The 10-20mm is a cracking lens, but in some respects in is quite limiting.
The 18-55 will be fine for the normal landscape shots. I've got no idea where you live, but just have a look online for areas nearby of 'natural beauty' or similar.
Like the photo I entered in this months comp, I know from reading online you can get some cracking shots from there, yes you have to be lucky with the weather too, but just keep going out and trying new places.
What sort of shots do you want the most? Landscape, cars, macro etc?