I just love astronomy images; it's hard to compare them with more "ordinary" landscape photos, but they surely have their own aesthetic.
You can find very
high resolution Hubble telescope images at: http://heritage.stsci.edu/gallery/gallery.html
They're freely downloadable, though you definitely need broadband or it'll take about a week.
If you click on the "index" tab, you can find some images that are huge; the largest (Carina nebula) is a gorgeous TIFF over a gigabyte in size. I couldn't resist; I printed it on an HP Z3100 at about 24x68" and have it on my wall now. It's mind-blowing.