You can check PhotoDune. I sell my pictures there as well: Ekushey | PhotoDune

With the advancements in digital photography these days it is not too hard to take good quality images yourself if you have the time and the means. I would recommend this approach for a more accurate perspective of your company as you know it better than anyone else. However, having said that you may be too busy to find the time so here are some links for you:

Morguefile.com free stock photos
StockPholio.com | Free Stock Photos
The Leading Source Of Free Stock Photos - freeimages
Free Photos - Free Images - Free Stock Photos - FreeDigitalPhotos.net
Stock Photos free for commercial use by StockPhotos.io
Pixabay - Free Images
Royalty free images, photos, vectors and videos on Fotolia
Stock Photos, Royalty Free Images, Vector Art, Footage | Depositphotos

Depending on your industry, you might find US government official photographs which are usually released without restrictions. Health, science and safety related are abundant.

Check out the wikimedia commons. They have a ton of public domain images. You can also do a google image search, click search tools, and specify the license type in the Usage Rights dropdown.

Wikimedia Commons

I like depositfiles.com - they have tons of image, most cost $1 to use