I've made three trips to Paris, and each time, I bring along the latest version of the Rick Steves' guide. Rick is kind of a controversial figure on frequent flyer travel boards. His guides tend to simplify touring by including mostly HIS favorites, but that's precisely why I buy it first time I'm visiting a new place. His books are easy to read, and they give the nitty gritty details about how to get from point A to point B. That information is often lacking in other guide books, and when I'm going to a place for the first time and will be there just a few days, sometime less information is more.
I don't usually repurchase his guides after the first trip, but the Paris book still comes in handy when I'm navigating around the city and want a reference to the attractions. Rick's listings of hours and closings is more apt to be correct than other guides because he really does update it ever year. Also, the book contains tours of many of the museums as well as walking tours of various areas of the city.
I find the food and lodging sections less helpful, as I do my own research on those on travel message boards. I supplement Rick's Paris book with other guides, but for carrying around for quick reference, his is hard to beat.