Joanne Liebeler's "Do It Herself" as a housewarming gift. For a first-time homeowner the book does a great job at explaining how a house works and why the things you can't see are so important.
For me this was especially useful since (for the most part anyway) I had no idea how a house worked. The author uses simile to compare a house to the human body. A house has the actual structure, a "respiratory" system and a "nervous" system--just like we do.
In addition to explaining how houses work Ms. Liebeler also gives a list of tools that she has found especially useful in her home projects and goes over some basic projects that a new homeowner might be getting ready to tackle. Some of these seemed way too complicated for me, mainly because they required power tools which I'm still wary of using. It's still fun to read about the projects though and the book will be a great resource if I do decide to attempt any of the projects she mentions.
These are a few other books that I've heard are good for homeowners. Most of them will likely find their way to my bookshelves someday. The last one was recommended on the blog Young House Love and is actually in my house right now waiting for me to sit down and read it (as I've mentioned before my lawn needs a serious makeover).