Following are pretty standard and very famous options:

1. If you are looking for blank images with dummy text, use Placehold.it.

   placeholdit.imgix.net/~text gives following:

   

2. If you want real random images, use LoremPixel

   Something like this http://lorempixel.com/400/200/ would generate following:

   

   This http://lorempixel.com/400/200/sports/ would generate following:

   

   Only disadvantage in LoremPixel is that it has no support for HTTPS.

3. PlaceIMG also gives you real random images.

   This https://placeimg.com/200/200/any will generate something like following:

   

4. If you like kittens 😉, use {placekitten}

   placekitten.com/200/300 will generate :

   

5. And my favorite is Unsplash. Apart from simple placeholder images, it also supports many image transformations like grayscale, blur, cropping with gravity, etc.

   unsplash.it/200/300 will give you following:

   

I hope that helps! :) Let me know if you find some more.

Do checkout HipImg as well (www.hipimg.com)

You can simply get a placeholder image using hipimg.com/350x200 and add a color using color code hipimg.com/350x200/03A9F4

Sorry for the late reply - this post comes quite high in Google.

I'e just released a Morgan Freeman based image placeholder site 😀

morganfillman.space