Here are the top most popular photo sharing sites.

1. Flickr

flickr.com

2. Cluster

cluster.co

3. 500px

500px.com

4. Shutterfly

shutterfly.com

5. SmugMug

smugmug.com

6. Google Photos

google.com

7. Zenfolio

zenfolio.com

8. Instagram

instagram.com

9. Photobucket

http://www.photobucket.com

10. Snapfish

snapfish.com

11. Imgur

imgur.com

12. DeviantArt

deviantart.com

13. TinyPic

tinypic.com

14. We Heart It

weheartit.com

15. Keenai

keenai.com

16. Canon Irista

irista.com

17. Twitter

twitter.com

18. ImageShack

imageshack.us

19. ImageBam

imagebam.com

20. Picasa

picasa.google.com

21. ImageVenue

imagevenue.com