I am not an organized cook. I have ten million cookbooks with one page dogeared in each. And then there are all the recipes I have emailed to myself.... Then one day I came across recipething. It is very simple and allows me to put all my favorites in one place! I put together a list of a bunch of the online recipe organizers - my favs are recipething and Real Simple's My Kitchen.

recipething
Are your recipes lying around in emails, Word documents, Crisco-covered cards and crumbling cookbooks? RecipeThing lets you organize your favorite recipes, share them with your friends, and use them again and again. A very basic but great site! A cool feature is the RSS feed of your friends' recipes. Free registration required.

Real Simple's My Kitchen
Real Simple lets you lets you save and organize recipes - both your own and those from Recipe Finder - into Saved Recipes. You can also save menus as well as customized Shopping Lists. Also useful: Real Simple's Daily Recipe RSS feed

A few more that are out there:
Epicurious' My Recipe Box requires registration but allows you to Save recipes from Gourmet and Bon Appetit to your personal Recipe Box, submit your own recipes, and share recipes with other "My Epi" Members. Many recipe RSS feeds available

Allrecipes My Recipe Box
My Allrecipes allows you to save, organize, and share recipes, meals, reviews, photos and more. Store recipes from Allrecipes, your cookbooks, magazines and other websites. Sort recipes by rating, source, title and date. Organize recipes into whatever categories you like and a dd private notes to any recipe. Free registration required.
Yahoo Food
includes "cooking with kids" from Kraft - does not have a recipe box but does keep track of all your recently viewed recipes at the bottom right in "Recent Activity"

Kraftfoods.com
has a personal recipe box feature that allows you to store all your favorite recipes in one spot - whether it's from Kraft, or a favorite from your family's kitchen. Use your recipe box to save, organize, print, rate, and create a Shopping List. More info on features is here

Food Network's My Recipe Box requires registration, has a limit of 50 recipes and has a disclaimer at the bottom: "Please note! Some recipes are only available for a limited time, and may be removed from your Recipe Box at any time. Please print recipes in advance."

Martha Stewart's website also allows you to "collect" recipes as you browse the recipes on her website. But you do need to be registered.