Easy YouTube caption creator
The Easy YouTube caption creator is designed to make it very simple to create a caption text file (.sub format) that you can then add to YouTube video files that you have uploaded.
This is something of a one-trick pony; what it creates is not rocket science, it's just designed to make it a little easier (and hopefully will encourage you to caption more videos).
There's an overview of this tool on YouTube.
Note: this tool is no longer being developed as YouTube's automatic captioning has somewhat overtaken this tool. If you already have a transcript and if the audio in your video file is clear enough, YouTube can probably work out the timings automatically.