Few things in life are free - but at Unsplash.com you can acquire 100% completely free high quality imagery for your website (Or for other uses).
The site has a plethora of high quality, well shot and modern imagery that you can use for practically any purpose. The size of the images is good (although they aren't massive - I doubt you'd be able to print these to a large size) and are perfect for websites and blogs.
The service doesn't require you to give credit either - but they do encourage it, and I think that's only fair given the quality of the work being gifted to the visitors. This is no ordinary stock photography service, you won't find awkwardly staged actors playing out a series of unrealistic poses for the camera - just natural people, places and concepts that look professional and are extremely easy on the eyes.
Here are a few examples - check out their website for more:
Credit: Ali Gooya - @aligooya
Credit: Thomas Litangen - @litangen