JustSubsPlayer is a player for .SRT files. Unlike other software, it does not require a video file, so it can be used to add subtitles to online movies or TV series, even if they are flash-based videos.
The projects contains a sample SRT file.
This is a good site where you can find subtitles: http://www.sublight.si/
Automatic file registration is not available yet, but you can right click a SRT file, choose Open with, browse for JustSubsPlayer and tick "Always use this program"