She writes on her blog (she graduated from LJ to A Real Blog) (sensibly located at RobinMcKinleysBlog.com) that she wants to write the sort of books "that people take to bed with them, read in the bath till the bubbles are all gone and the water’s cold. Or choose to go with them on long gruesome plane flights."
For me, Sunshine is quintessentially that sort of book. It's a comfort and a delight, and - in this crazy life I lead - she can count on me to keep buying copies. Through the miracle of gift-giving holidays I have arranged for it to be shelved at my best friend's house and in my boyfriend's apartment (I made him read it once, and I've read his copy twice this year). I've got a copy at my parents' house, one in my apartment, and another that sort of "floats." That sounds like overkill until you realize I have five copies stashed in four houses (three of which make up my "residences," in various forms), in four different states splayed diagonally across North America (Alaska to Florida. Whee).
That floating copy exists largely so I have a spare for airplane reading. After a horrible flight a few years back where I spent hours on the tarmac strapped in, in front of an unsupervised four year old with shiny (pointy!) new cowgirl boots and an apparently deaf little sister who needed to be entertained, I don't travel with only new books. If they fail to meet expectations and work isn't engrossing enough, then I am stuck with nowhere to go. I carry one staunch favorite (often Sunshine) to hide in, when those disasters strike.
What books meet that criteria for you?