There are other such sites. Some with good photos have gone on to charging a fee, others have tons off snoozer-point-and-shoots with bad quality. But, there is some gold to be found at MorgueFile. Many photos are high-resolution, press-quality gems.

One particular photographer always has some treasure:
Check out Clarita's photos.Clarita has over 3,000 shots, and really has an eye for this craft.
Now just because you can use the image, doesn't mean you own the copyright. Give the artist a photo credit if you use their photo online or in a publication. Some may want you to shoot them an email first. (That's Clarita's fish photo btw, clarita1000@virgilio.it)