What are useful ranking algorithms for documents without links?

Question

I\'ve looked at Algorithms of the Intelligent Web that describes (page 55) an interesting algorithm - called DocRank - for creating a PageRank like score for business docume

Answer 1

I've done some additional research on the topic and found the Wikipedia entry for the Okapi BM25 algorithm. It also has a successor BM25F that takes document structure into account, but this appears to be more relevant to HTML/XML.

BM25 Incorporates:

1. average document length in the collection,
2. length of the particular document
3. term frequency

Finally, the Wikipedia entry links to a Lucene implementation.

Compared to @Doug's answers above this appears to be a more complex algorithm to implement.