.... for photos for use on a website and for creating site headers? I Personally either use my own photos if I have something suitable or purchase from a microstock site - no getting into trouble that way.
I haven't used it much, but whenever I do need to, I use iStockPhoto.com. I get the smallest picture possible that I can still use, so my price ranges.
I don't use pay anything for photo's. I try to grab any photo's I need off free stock photo website's and what not
I almost never need pictures for my headers but when I do need them I either snap them myself or go to free istock websites
If I had a camera, I'd use my own. Since I don't, either free stocks off google, or the stock exchange.
I have my own camera and once thought I'd never use a stock photo place, but have since changed my mind. I use the stock photo places to get ideas, if I find the perfect image, quicker to pay the dollar than to set up and find whatever, and take the picture. I'll probably add some of my photos there too. Other times it is a picture I want to take and I know it will be unique.
Istockphoto works for quick, inexpensive, quality photos. A word of caution though, you do need to be careful about which images you pick. Sometimes they are blurry, but that doesn't always come out in the thumbnail preview.
I've had great luck with Lucky Oliver lately. Similar prices to IStockPhoto, good and improving selection, and great interface. http://www.luckyoliver.com/
If I can't find any free stock photos, maybe around 1 - 3$ is spend on stock photographs. It's best to keep things safe and not rip any photographs off anyone.
Am a longtime customer of photos.com and istockphoto. I am alway sready to pay > $5 if the picture is worth it.