I engage in a constant search for great free photos to use as featured images for my blog posts. I used to love sxc.hu but the site etiquette for “free” photos strongly encourages you do what the photographers want and link back or acknowledge where you have used the image. No problem if you are looking for an occasional image to use but when the process of the search is at least a daily one all the extra “steps” in acknowledging photography can add time that I just don't have to the search process. This is similar to certain Creative Commons licenses. Remember when cc meant carbon copy? But I digress. I have not found a great way to search for Creative Commons licensed photography.
But there is morguefile.com
Everything image on Morgue File is free to use. Read the fine print even here, but basically other than use in a standalone fashion, you are free to use the photos on the site without attribution. For folks who are not making money from their blog, this can be a goddess-send. If you are creating a professional site, you probably want to invest in great photographs to enhance your great site, but when money is a real concern and limiting constraint, Morgue File is your enabling constraint.
The photos on the site are not all second rate. Some are not professional quality. But some are great quality and are used to entice you into viewing that photographer's site or professional work for sale on other sites and purchase some of those images. I found these images on Morgue File when I was looking for fall images.
Of course you can always just take your own pics too!