Biology (Campbell Biology)

Yep, that's the one I was going to say :-) "It goes really deep" is, unfortunately, a relative description. Half-way through my undergraduate studies, I had pretty much outgrown it and needed more specialized books. Nonetheless, it is a superb entry-level college textbook that covers the entire breadth of modern biology. The text is very understandable and gives more background information than is needed for a typical introductory lecture to any given topic (while still emphasizing the salient points so you don't get confused). Apart from the above-mentionend interviews, it also includes sections on current methods in biology, which are pretty handy when you're new to the field. Plus, the illustrations are simply excellent: pretty to look at and a huge help for understanding. On the whole, I find it to be one of the most aesthetically pleasing textbooks I know. (Beaten only by Futuyma's "Evolution".) My best investment in university so far!

A bit late to this party, but: Campbell et al.'s "Biology" is the best textbook I've ever read. It starts at entry level but goes really deep. Everything is explained very well and beautifully illustrated. To add context to the "hard" scientific content, there are also interviews with leading researchers in biology who provide their points of view on the main themes of the book. There is a bewildering confusion of editions and versions of this book, but look for a book called "Biology" or "Campbell Biology" with Neil A. Campbell and Jane B. Reece in the author list, but not necessarily listed first. There is what I believe to be an abridged version called "Biology: Concepts and Connections", and something called "Biology: A Global Approach", which may just be the name for the newest editions.