as others have mentioned I second the EF-S 17-55 f2.8IS USM, that is right about your target budget new, maybe a little over, although you can probably find one used for around $900. the 24-105 f4L is also a good option, but maybe not wide enough on crop for your landscape needs. Sounds like you may have the 18-? IS zoom kit lens, either variations aren't worth much more than $250 used (and that may be even stretching it a bit), so just keep it and use it when you need the extra reach or want to take something on vacation that you don't care if it gets lost/stolen/takes a swim...