Google, Yahoo, MSN, & Teoma have compiled a huge link graph of all the sites on the Web that are accessible by their spiders. I can barely fathom the depth of such a link map. I tried to build something that really does a job of uncovering the link structure around a specific domain name, I named this free tool Google Link Popularity Analysis Tool. But it is limited, it only looks at the Google link command and then branches out from there. The limitation is annoying, it doesn't let me get the complete picture of the linkage data around a particular domain.
I would love for Yahoo to open an API, which I can use to make it possible to really get a picture of the true linkage structure of a site. I probably would want to combine Yahoo, Google, MSN, & Teoma - but the likelihood of anyone outside of Google opening a free API is small (within 2005). Now, would I pay? I think I would, but I know many would not even talk to me about licensing such data. But I would strongly consider paying a per 1,000 query limit fee to get at such data. Others at WebmasterWorld are discussing this topic.