"I think RATM, Korn, Slipknot, Linkin Park and maybe Blink182 will be the only rock/metal bands that will be remembered as classics of the 90's"
If you mean bands that were around in the 90s the I doubt Linkin Park and Korn (although Korn are good) will be remembered to that high of a degree.
Faith No More, NIN, Deftones, APC, Tool to name a few.
Although some of those are only gonna be remembered by those with enough knowledge.
-AC
The obvious ones: Smells Like Teen Spirit, Closer, Creep etc.
Possibly Disarm by Smashing Pumpkins.
I'm sure RATM will be remembered, I'm not sure for which song though.
However, as much as it pains me to say it, right now I don't think Tool/APC/Opeth/Deftones or any number of my favorite bands have any songs which have been big enough individual singles that will go on to be classics.