You could try mine: http://www.packtpub.com/apache-solr-for-indexing-data/book . It's quite popular and comes with a GitHub repo for the examples.
How do you feel that a huge number of potential buyers gets your book today for free?
As to getting the book for free, please do. I have something even more interesting in the works. I would love for you to read my book, get excited about Solr, get on my mailing list http://www.solr-start.com/ and pay me for my next project eventually.
The authors usually do not get rich of the books (though I did cover my tiny advance and more). The rest of the conclusions is left as an exercise for the reader.