If you need free stock images for your website, blog, presentations etc. then the best free site around is stockXchng.
StockXchng has been around for some time but really seems to have come into its own over the last year.
They claim to be the “leading free stock photography site” currently listing 313484 free images with 400 - 500 new images being listed every day!
They have over 25000 photographers submitting images and a lot of them are very good!
I have found a number of good free images suitable for use in banners etc.
There are premium or paid images listed too, starting at $1 per image. These are actually hosted on a sister site StockXpert are to a very high standard.
If you are prepared to pay one or two dollars for your images then istockphoto.com is also a very good source of stock images, with a much larger selection than stockXchng / StockXpert but alas, no freebies.