dotSUB is an online service that allows you to upload videos, and makes it very easy to add subtitles (closed captions). You can add them in more than one language if required - in fact you can allow anyone from around the world to translate the video.
I've added our most downloaded Web Cats episode, and added subtitles just in English for now. It's embedded below. Click on the up and down arrows on the bar at the bottom of the video to move to the subtitled version.
Is was quite a quick process to add the transcription that I'd already created, as dotSUB allows you to use some helpful shortcuts.
The 'RSS in Plain English Video', embedded below, has been translated into several languages. Again click on the buttons on the bar under the video to flick through the languages.
More information about subtitles and other ways of making online videos accessible are available at webaim.org.