here are my suggestions:

sonic youth - teenage riot
dinosaur jr. - freak scene
soundgarden - like suicide/jesus christ pose
fugazi - waiting room/forensic scene
radiohead - paranoid android
mr. bungle - carousel
Husker Du - pink turns to blue
Mudhoney - touch me im sick
smashing pumpkins - bullet with butterfly wings
Pixies - Debaser

yeah i agree with you about the SP song... maybe... soma?

and i needed to include a mr bungle song...

when i hear the term 'classic' in regards to any type of popular music it makes me think of what will be heard on the radio in 20 years not necessarily my favorites. as such my pics for alt-rock classics...

soundgarden - black hole sun
smashing pumpkins - disarm
alice in chains - would?
nirvana - smells like teen spirit
pearl jam - better man
red hot chili peppers - under the bridge
jane's addiction - been caught stealing
blind melon - no rain

nah i meant classic for the alternative crowd.

dEUS, "Suds & Soda"
Fugazi, "Waiting Room"
Pavement, "Stereo"
Pixies, "Where Is My Mind"

ahh in that case i'll give the must listens for the bands i listed

soundgarden - head injury
smashing pumpkins - pissant
alice in chains - godsmack
nirvana - very ape
pearl jam - do the evolution
red hot chili peppers - sir psycho sexy
jane's addiction - pigs in zen
blind melon - galaxy

I was just listening to that track today. What a tremendous song. Love the Geddy Lee reference.