This is, by far, one of the most frequently asked questions I receive. There are two primary reasons for my not including one-step sparring among these pages -- one personal and one practical.
The practical reason is actually two-fold. First, there are already some very excellent books on the subject in print. Hee Il Cho publishes an excellent book on one- and three-step sparring that can be purchased from a variety of sources (including his own site). Additionally, nearly any book that covers self-defense techniques can be used as a one-step sparring guide. (See: Where can I find instructional books on the hyungs?) "But these are print resources -- not online," one might argue. True. But I feel that text-based descriptions of one-steps would not be a benefit to anyone. They would require some sort of video (or other visual) presentation to be an effective teaching or study aid. Also, one-steps are not the same from school to school. Some instructors require specific techniques at specific belt ranks while others are more relaxed and allow for greater creativity.
This brings me to the second reason. I come from schools that stressed the student's role in developing his/her own one-steps. All the combinations of techniques that I use for testing were developed by me. Sure, I got a lot of ideas from watching others, reading martial arts books, even trying to adapt techniques I saw in action movies into real life. But I developed and crafted every combination personally, whether it was in the dojang, in the gym, or just running through some ideas in my bedroom at the spur-of-the-moment. I'm not afraid to share my one-steps with anyone, but I'm afraid this will actually be robbing students of the entire process involved. I believe that making these things your very own is half the fun.
In absence of their coverage here on my site, here's what I recommend. If you are required by your school to perform specific one-steps for your rank, then the only place you can learn them and improve upon them is with your instructor and fellow students. If you are a member of the USTF, there is a small paperback guide that outlines all of the one- and three-step sparring requirements for each belt rank. You can order it online for $10 by clicking on these words to reach the appropriate site. Unfortunately, I am not aware of any such guides for the USTU or other Taekwondo organizations.
If you are looking for examples of one-steps or inspiration for creating your own, I would pick up virtually any textbook on Taekwondo. Nearly every one contains examples of self-defense techniques that can easily be adapted to the one- and/or three-step format. I would also recommend that you not limit yourself to searching only Taekwondo resources. There are many fine books offered by such clearinghouses as Century Martial Arts Supply and Asian World of Martial Arts that cover a wide range of subjects and styles. Any of these could provide you with a variety of options for developing your own combinations and techniques.
Lastly, don't be afraid to be creative. Don't be afraid to try something fancy. Don't be afraid to do something different, something that no one else in your school -- even your instructor -- does. Don't get carried away at the expense of solid form and technique, but don't let yourself be restricted by the norm either. And practice, practice, practice. Anyone can do a one-step that they've seen every other student before them do. But, if you want your own creations to take hold and capture someone else's attention, you have to be able to make them perfect on your own. This often requires months and months of effort just to get a single one-step right. That's okay. I recently visited the very first master I had the pleasure of studying Taekwondo under. His students still do some one-steps that I made up in the late 80's as a green, blue, then brown belt. 20 years later, I don't know any of his current students, but they're learning these combinations that were good enough to be passed down, practiced and perfected.