Open Source Search Engines (comparison)
A comparison of ten (10) open source search engines.
Appears as an appendix to Modern Information Retrieval, second edition.
I probably don’t need yet another IR book.
But the first edition was well written, the second edition website includes teaching slides for all chapters, a nice set of pointers to additional resources, problems and solutions is “under construction” as of 27 July 2011, all of which are things I like to encourage in authors.
OK, I talked myself into it, I am ordering a copy today. 
More comments to follow.