I'm with Brainy Gal. I've used stock xchng for years with a lot of success for certain things. When you are ready to pay just a little bit and get even more high quality photos istock.com is my exclusive choice.
Sometimes, the copyright notice stated that one cannot use the copyrighted information without attributing it to the author/photographer, etc. I have had a blog up, for about a year and a half (not related to my business) and every image that I used contains an attribution. I've seen way too many sites, some from folks that I know, that do not put an attribution on images that they use. That's a recipe for potential disaster.
My favorite is morgueFile. I like that you can filter the type that you want ahead of time and don't have to look at the specific license for each picture, after you've decided you want to use it, only to find out it is unusable. They have a very large selection and the photos are good quality.
Here is their license statement for their free photos, "You are allowed to copy, distribute, transmit the work and to adapt the work. Attribution is not required. You are prohibited from using this work in a stand alone manner."