It's a GREAT idea to shoot your own stock images so you have exactly what you are looking for, but sometimes that isn't an option. There are lots out there and I've written about 5 FREE Stock Photo Sites before.
Before you go wildly downloading images to use, be sure to read the licensing and rules and be certain you're willing to work with those. Do NOT search for an image and download it for your project - using search engine images without proper licensing / permission is wrong and illegal. Don't steal other people's work.
Here are some to get you started
Captured By Carrie this site has animals, objects, textures and backgrounds. There are single items and bundles and the prices are good. Most of what is on this site is already extracted so that will save you time!
PixelSquid has design ready objects that let you to unleash your creativity. Improve the efficiency of your workflow with photo-real objects available at any angle with perfect transparency.
Freeimages FREE has lots of free images for you to use. Some are higher quality than others, but there are lots and lots to select from so you should have something that works for your project.
Adobe Stock single images start at about $10 ($9.99 like Macy's Bargain Basement) and there are subscriptions available too. The photos are beautiful and you'll be able to preview them first before purchasing to see if they work for you.
Unsplash FREE high-resolution images for you to use. All photos published on Unsplash are licensed under Creative Commons Zero which means you can copy, modify, distribute and use the photos for free, including commercial purposes, without asking permission from or providing attribution to the photographer or Unsplash.
Creative Market ready to use designs to help you get your creative on! Ready to use graphics, fonts, themes, photos and more starting at $2.
Pexels FREE All photos on Pexels are free for any personal and commercial purpose. All photos on Pexels are licensed under the Creative Commons Zero (CC0) license. This means the pictures are completely free to be used for any legal purpose.
Morgue File - FREE photos for commercial use.
No Backs - FREE This is a time saver! No backs on the images. Have you ever found yourself struggling to find a stock image with a isolated and clean transparent background? Or maybe you have wasted hours of your time trying to remove the background from an image? Graphics Designers like photos images with copy space, or space around the image where they can add text or background images, or just a simple color to match their publication or website, We are giving you the image ready and clean isolated on transparent background, Please enjoy our collection.
Deviant Art - The largest online art gallery and community. There's lots of variety and almost anything you might imagine needing. Founded in August 2000, DeviantArt is the largest online social network for artists and art enthusiasts, and a platform for emerging and established artists to exhibit, promote, and share their works with an enthusiastic, art-centric community. We have over 38 million registered members and attract over 65 million unique visitors per month. Our members — knowns as deviants — upload over 160,000 original art works every day, everything from painting and sculpture to digital art, pixel art, films, and anime.
BlogPiks - Thanks to Stuart Miles for sharing this site in the comments. Free Images For Your Blog, Website, Social Media Or Presentation.