It's fairly simple to construct your own. I wish I could add pictures of mine, but our main computer is down right now, so you'll just have to use your imagination. :)
I bought an inexpensive, three ring binder and used dividers that have pockets on them to mark the sections. I use page protectors for everything so the paper is protected if I decide to take it out in the garden with me when I'm planting. The reason I use dividers that have pockets is so I have a place to stick notes, or articles if I happen to be out of page protectors. That way they are already organized and ready to file after my next trip to the office supply store, instead of sitting on a desk, or in a drawer somewhere.
I have the following sections in my notebook:
Garden plans - I literally draw the layout of the garden (you could use graph paper) and
write in where things are planted. I write notes on the back of the "map".
Things like, how a particular variety performed, or whether or not you
saw a benefit from a companion planting.
Tips - This is where I store charts for crop rotation, spacing, and compainion planting.
Pests - Info. on pest problems and organic solutions/suggestions.
Other problems - How to diagnose, and organically treat other problems that you may
run into, like fungal diseases or nutrient deficiencies.
Articles - Sometimes I run across an article that covers a wide range of information, which
makes it difficult to file in any one section. This is where those go.
I've seen many people talk about keeping a gardening journal and I can wholeheartedly agree that it is enormously helpful. If you're not already keeping one, it'd be a great idea to get one ready before the next planting season.
I've linked this post with the Farm Girl Friday Blog Fest.