...don't start an excel file...there's something so much better already out there if you're a nerdy book person (no offense, I'm talking about myself!). It's Librarything.com. I've got all my (ahem...er...5,000) books on there, and I love it, love it, love it. You enter your books by just typing in the ISBN, or maybe the title, or maybe just a word and the author name--whatever works for you--then everything else comes up automatically--a photo of the cover, the author, etc, etc, etc. If you want to be truly anal (what? who? me?), you can add a whole bunch of "tags" that you might use later to look up the book (i.e. "dinosaurs," "letter A," "bottom shelf," whatever works for you!) Then when you want to look at your list of books, you can organize them however you want (so if you wanted to, you could have it alphabetize your list, and then make your shelves match). It's free up to 200 books, and then I think it was $25 forever for the rest. (That was years ago, so it may have changed.) If you want to be really like a librarian, you can buy a "cue cat" from them (my friend gave me one!) and it scans the bar code on the back of your book so you don't even have to type in the ISBN (totally worth it if you were going to do your whole collection). My virtual library is gorgeous. :-) (You can see mine
here, if you want to see how it works.)
Now as for my shelves...I'm a mess. I've got some organized by topic, some by favorite authors, some as sets, some just randomly, and many in a heap on the floor that don't fit in the shelves. But librarything helps me remember what I have so I can go in search of it.