I’m really enjoying the “Identities” page on WorldCat. As you might remember, back in 2003 the library service opened up its records to the web (previously only those at subscribing libraries could see the results). I never noticed it before, but their Identities service pulls together lots of useful information about well known people, such as what the most popular works about them are, names of related people, etc.
I really like the “publication timeline” which shows how many works by and about the author were published in each year (also differentiating between works they published while living and posthumous publications). Here is the chart for Clifford Geertz:
And here is their tag-cloud for the top American anthropologists by number of holdings in libraries:
The service is still in beta, but as it grows I can see it being an excellent supplement to Google Books and Wikipedia, especially for getting a handle on a new author you might never have heard of.