You've got a lot of unused whtespace around "HD Wallpapers". Perhaps you have plans for that? You might want to change that to read "HDNewWallpapers.com", and/or do a spiffy logo. The search function doesn't seem to work. Perhaps you are a Mac user; but when I click on a wallpaper, I see an X in the upper-right hand corner, and I expect it to close the graphic; but instead, it enlarges it. There is a separate X to close it, but I didn't notice it at first. A different icon for enlargment might be helpful. It might be nice to provide for a caption for each wallpaper, instead of the name of the article below each one. One thing which I applaud: Most light-boxes behave badly when you try to do a mouse-wheel scroll to enlarge what you are looking at. Yours works when you do that, and has a separate enlarge option. I always prefer Disqus comments to allow the guest posting option. They can still give a username and caption; but don't have to sign up or log in to anything. Instead of putting "Free Download" after all the free pics, you might put "(Premium)" after ones that are not free instead, or even just "*", with an "*" followed by "Premium wallpapers" or some such.
Obvious movie wallpaper requests: "The Matrix" most importantly, but also "Star Wars Episode III: Revenge of the Sith" would be nice. "Lawnmower Man" is also very much of the Digital Age. Would space and/or science wallpapers go under "Nature"?