This is my system for keeping track of the things I want to cook. I use a composition book with a green-speckled cover, probably purchased from the Rite Aid Drugstore around the corner. When I find a recipe I want to try I note the name of the recipe, the book and the page. When I've made the recipe, I check it off.
The compostion book is divided into time periods and occasions (summer, fall, Thanksgiving, Christmas, etc.) so if I see a really great recipe for tomatoes in November I simply enter it under "summer" and next summer when I refer back to my notebook, there it will be. Of course, I now have multiples of the same category because I've run out of room on the original pages.
I've been using this for about a year and it works fairly well. Prior to that as I went through a new cookbook I would write down any recipes I wanted to try on an index card which I sometimes put in the book and sometimes collected elsewhere. I never did a get a definitive system down with the index cards, and it turned out to be a short-lived system because it was fairly useless.
Before the index cards I went through a period of copying any recipes I wanted to try but that resulted in a lot of paper to paw through whenever I wanted to see what was in the queue and the system was never efficient or satisfying. And before that I didn't really have a system other than keeping in mind what I wanted to try or piling the cookbook with whatever recipe I wanted to try in the kitchen. Neither was particularly effective.
For some reason I'm usually able to lay my hand on whatever book I want immediately but the notebook itself is harder to keep track of. It floats around the house between my bedroom where I often read cookbooks in bed at night and the kitchen where most of my cookbooks are stored but sometimes it gets set down in places in between and I find myself hunting for it.