Thread for the manga of Toaru Kagaku no Railgun (とある科学の超電磁砲/A Certain Scientific Railgun):
For more information on the setting, look at the anime thread
http://forums.animesuki.com/showthread.php?t=67218
There isn't much to explain other than that. Railgun is a side story focusing on Mikoto.
There are two volumes out.
There seems only to be one chapter translated out though.
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Have not bought the actual volumes, but since it was just a click or two (or five or six) away, I read the first chapter.
It's only one chapter, but I've taken a liking to it. Probably just because the Mikoto's electric abilities are so... devastating (and appealing).