What about Joy Division and The Birthday Party? This is the first I've heard of Sisters of Mercy.
*cough* *splutter* *cough*
WWWHHHHHHHHHHHHHHHHHHHHHHHAAAAAAAAAAATTTTTTTTTTTTTT????
You need to start your education RIGHT NOW!
This is gothic rock (and, incidentally, some of the greatest pop songs ever written):
http://www.youtube.com/watch?v=eZQRv7o49Lc
http://www.youtube.com/watch?v=ROnXv7Z7v28 feat Ofra Haza
http://www.youtube.com/watch?v=qDuW3NvjqJY
http://www.youtube.com/watch?v=qWvOHT0zfXY
It's basically if you took the worst theatrical excesses of Meat Loaf, filtered it via The Addams Family and applied it to catchy rock. Joy Division and The Birthday Party are post-punk.
Dealing with so called "Gothic" symbols and ideas I think of the demonic stuff dealing with skulls, and macabre scenes/depiction of gruesome things.
No, that's not "real goth" - I regularly went to goth clubs for years and really it was more kitsch and Halloweeny. Again, the Addams Family vibe. It's not so much inspired by 12th century churches as by Mary Shelley and Bram Stoker's Dracula. It's way too camp to be gruesome - put it this way, a goth told me, "I've never been in a fight - I might break a nail!"
I think of this guy. http://www.downfallguild.org/sites/www.downfallguild.org/files/images/Goth%20Hula%20Hoop.png
Ha! No, Slipknot aren't goth at all - he'd have to be wearing a Bauhaus t-shirt. If you're rooting around for an image, The Crow was pretty popular "in my day".