I’d like to share with you an image resource I’m using for a couple of years now. Textures.com have a big library of textures, ranging from technology to architecture, landscapes, nature, fabrics to all sorts of stuff. They offer a free membership with a 15mb/day download limit and various packages for professionals and companies who need more.
I bought myself a cheap 100mb/day plan, which gets me through all my jobs and projects fairly comfortably.
Their images are pretty high resolution and especially photographed to work as neat as possible for texture artists (mostly flat angles and or scans). Many textures are already masked, so they can directly be placed into whatever you are cooking up.
Get an account and start browsing here: http://www.textures.com/