You sound like a very organized person! The plant book is a great idea; I have something similar where I keep the plant tags in plastic pages that have pockets (like kids use for collecting hockey cards etc....) I use little index cards to note important information about the plant (pruning, feeding, where I got iy from, when I planted it and anything else that seems relevant!) and I tuck the cards in behind the tags in the pockets.
When looking for information on plants, I've found that I use multiple sources of information. The the web sites I go to most often are the Ohio state University Plant Dictionary at:
http://www.hcs.ohio-state.edu/plants.html
and the Heritage Perennials site at:
http://www.perennials.com/
The OSU plant dictionary allows you to search by either botanical or common name. It has pictures of the plants with a brief description and then, at the bottom, of the page, a link to their detailed text database on the particular plant.
Heritage Perennials also has good pictures and very concise listing of key data about the plant. They have an excellent 'Advanced Search' function which allows you to select key characteristics you're looking for in a plant and it'll list plants that meet that criteria - a great tool when you're looking for just the right plant for a specific spot. In this week's articles on this site, there's one about their 'top 10' plants for this year. It has links to their data on those plants so you can sample the information on that site when you read that article....
The other key reference source I use is Christopher Brickell's The Gardiner's Encyclopedia of Plants & Flowers. My copy is fairly old now but you can still find this book, or a similar Reader's Digest book, if you look. It's not cheap though - books like that tend to be $80-$100+...
For wildflowers or native plants, The New England Wildflower Society's Growing and Propagating Wildflowers is an essential reference. They also have a web site at:
http://www.newfs.org/index.html
Everybody has their own favorite reference sources, so I'm sure you'll get lots of different suggestions...