I don't know about you but I have spent some time in the past looking for high resolution photos for using as wallpapers. I like nature pictures for instance. But that wasn't very easy. I usually didn't find that many pictures with high resolution available (most of them are 1024x768 maximum) and many of them had letters and ads super-imposed. Sometimes I had to go through sites full of pop-up windows and annoying ads.
I found a way to search for high resolution pictures much more easily and cleanly. I'm currently looking for lens for my new Canon EOS 400D (post about it soon) and have found that many sites with reviews about photographic lens, also include some samples, pictures taken with the lens in review. Most of them were taken by professional photographers and are really good. The pictures are also, most of the time, with the highest resolution the camera used supports which is pretty big. Here are two small examples: 1 and 2. Don't publish the pictures you find anywhere though. Use them for your personal use only. There might be copyrights involved.