Update: Years later, let me add my own ad rate calculator to the list below.
Occasionally, I see people asking how much they should charge for either text links or graphic ads on their site. Frankly, there really isn't a "standard" chart out there, although that would be a useful thing to have. However, I've compiled a list below of several link/ad pricing tools that may help you get a ballpark range of what your site is worth in terms of advertising pricing. Expect to see the occasional wide ranges from each tool, but some information is better than none, when trying to determine what price to charge.
And just in case any search engine reps are reading this, I am not advocating anything like selling PR. This is a post to help people monetize their site via legitimate advertising...you know...like in so many other real-world markets...newspapers, magazines, radio, television, um, and search engines too!