Creative Market is an online marketplace for handcrafted design content from independent artists and designers. On CM you can buy digital goods which you can use in your personal and commercial projects. Have a look at my profile, a link to my shop is here:
Storybird is 'reverse-engineering' the picture book. It's a storytelling community that curates artwork from illustrators around the world to inspire writers of any age to turn those images into stories. I have my digital artwork on Storybird. To write a book with my art, go to my profile, click "use this art" at the upper right hand corner and start writing:
Of course you can always contact me directly if you'd like to use any of my images privately or commercially, or if you'd like me to customize an image for you. You can pay via Paypal or Credit Card, and I will send you a high resolution JPG and/or a vector file in return.