Use Google and Yahoo search to get the best wallpapers of your desired size.
For images larger than 1024X768 resolution.This trick was discovered when i wanted to see extra large images of Aishwarya Rai and i finally ended up discovering this - click here
You could never imagine how good these images can be, i figured out a few images having such a detailed resolution, I was so amazed.
On google .com
->Go to Google.com
->Click on images Tab
type the name of the name of person or thing you want pics of.
->Now to see the best quality images click on the drop down menu saying
Showing- and select Extra large
Same trick works in yahoo
->Go to image tab in yahoo and select..
->Wallpaper for searching images of size - 1024 X 768..
Please do comment and ask if help needed.