Stock photos may be the bane of the Internet, but classy stock photos make a site look more professional. But you need photos that look unique, because generic ones aren't classy. I'm providing resources below where you'll find great free and paid stock photos that stand out.
Free stock photos
A great collection of professional photographs with a liberal license. I’ve even cropped out smaller sections of the photos that looked good since they are so detailed.
Use the creative commons image search. Be sure to read the license for each photo. Some of them require attribution or have other stipulations. However, many photos are in the public domain.
Needless to say, I don’t need to rehash a list that’s already covered in great detail in this post. Dustin compiles a list of sites for free stock photos here (some of them require attribution - it's noted next to the link). Also, I noticed this page is updated regularly with new links since I started visiting it.
Paid Stock Photos
A google search for “stock photos” pulls up the most popular paid stock photo sites. You’ll need to sign up for an account and use your credit card to purchase photos (rather than apply the nifty right click and Save as technology). Be specific with your search terms because these sites have zillions of photos. A few of the biggest names are:
A Word on Google Images
It’s tempting to search Google images and take your pick from the results. However, Google images pulls up whatever it finds across the web. Images are usually copyrighted, or at least the owner intended them to be copyrighted. The downside is you don’t know this -- the search results don’t send back any copyright information.
So be wary about copying and pasting those photos on your site. Perhaps try to contact the webmaster and ask if you can use their photo.