Poll: What's your most indispensible knitting book?

I have accumulated a lot of knitting books--some more useful than others. Sometimes I go through phases of what the Darling Marxist Curmudgeon refers to as 'late-night clickety', which is basically ordering things from Amazon.com in the wee hours of the night when judgement is impaired and wants and needs are amplified. It usually goes a little something like this: Jane Q. Knitter raves about a certain knitting book on her blog, I follow the link and am instantly seduced by the lurid photo and salacious reviews on Amazon.com [N.B. I do not normally promote large multinational corporations and/or big-box stores and always root for all that is marginal, indie and local, but there are literally no independant booksellers where I live, so please forgive me.]. And then I order it. And I forget all about it until I arrive home from work (hopefully before the DMC) and pluck the package from my porch. After several moments my memory is jogged and I remember, "oh. it's that book". And then the package sits there for anywhere from 15 minutes to 36 hours, and I open it. Blah blah blah-blah-blah. Usually the book is somewhere between fine to mildly intriguing. The most recent late-night clickety produced a book that was so much more than that, as it is (are you ready?) literally the best knitting book in the entire world. I have been waiting for a book like this for a very long time. Charlotte Schurch's Sensational Knitted Socks is nothing short of a miracle. It's amazing--everything about the book is helpful. Similar to the Ann Budd books, the patterns are all based on gauge, which is incredibly freeing. Like the Vogue Stitchionary series, there are close-up images of all the stiches featured in the book. Schurch also provides instructions for each pattern using 4 dpns, 5 dpns and two circular needles--again, totally useful. Her book is so strong because it can be adapted for use by any knitter, no matter what her style and ability. Simply put, this book is indispensible for any sock knitter. I [heart] Sensational Knitted Socks!!
My unbridled enthusiasm for this tome has me thinking about knitting books in general. Some are average, many are not worth the money, others are riddled with errors, many are all flash and no substance and a great deal of them feature impossible patterns. And yet somehow others are indispensible. What makes for a good knitting book? A balance of technique and artistry? Awesome photos? A big-name celebuknitter? Tell me: what is your most indispensible knitting book?