I use an excel spreadsheet and list the titles of all the pages I've created, are in progress, or plan to do in the first column.
The second column is "color scheme" (pages I haven't created yet, I leave blank).
Third column is decoritve theme (emblishments, like flowers, stars, spirals, etc).
The fourth column is "Needed Supplies" I list any supplies that I need to finish the page. I try to be as specific as possiable including the product name, maker and description (helps if you ran out of lettering and you want to get more of that specific lettering).
So when I go to the store or shop online, I'm sure to only get what I need and nothing more. Having the "color scheme" and "decortive theme" columns help me jog my memory of that specific page so I can shop smarter.
I also have another column on the spreadsheet called "work needed" which I leave myself notes on what has to be done to finish the page (great for reminding you of your vision of a page even if you a lot of time has gone by. And if you only have a certian amount of time to dedicate to scrapbooking, you can easily see if there's a page you can finish up in that time)