There are no sites which donot credit back. If you need HI-Res photos you can check at sxc.hu and deviantart.
You could use Google Image Search, then check the source/copyright of any images you find that you'd like to use.
Flicker, or if you are looking for some photos to edit in photoshop, just search for some stock packs, you will find a lot of them!
Don't use Google Image search -- just because there are images there, it doesn't mean they are free to use (and it's often difficult to find images that you can use freely there). Try Morguefile. In most cases you can use the images there for commercial purposes -- just make sure you read the photographer's comments (if any) to ensure that they haven't specified that there are restrictions.