^ When my UV filter broke, it got tiny glass dust inside the lens. I wouldn't use another one. I also don't know what kind of lens cap you have, but if you're shooting Canon, I highly recommend swapping out your lens caps for the Nikon center-pinch style. They stay in place much better (my Canon lens cap is somewhere in the Tasman Sea right now) and you can take them on and off without removing the lens hood.
If I went with two filters for landscapes, I'd get a circular polarizer and a graduated neutral density filter, which allows you to take more evenly exposed landscapes when the background is bright and the foreground is dark. If you're going for natural-looking shots rather than post-processed, I think a graduated neutral density filter is better than HDR (just my personal opinion, of course). Make sure to get glass filters, not plastic.