Obviously classic can be debated, but I would say there are many albums out there where the majority of fans would be in agreement: Here are two that I think most would agree fit the OP:
Led Zeppelin IV:
“Stairway to Heaven” “Black Dog” “Rock & Roll”
Marvin Gaye, What’s Goin’ On
“What’s Goin On” “Inner City Blues” “Mercy Mercy Me”
Obviously excluding greatest hits albums, comps, and all Beatles and Stones albums. 
Darnit, meant to include “When the Levee Breaks” on Zep IV.
“Who’s Next” with “Baba O’Reilly,” “Won’t Get Fooled Again” and “Behind Blue Eyes.”
The Freewheelin’ Bob Dylan:
Blowin’ in the Wind, A Hard Rain’s a-Gonna Fall, Don’t Think Twice It’s Alright
Bringing It All Back Home:
Subterranean Homesick Blues, Maggie’s Farm, Mr. Tambourine Man
Highway 61 Revisited:
Like a Rolling Stone, Ballad of a Thin Man, Desolation Row
Blood on the Tracks:
Tangled Up in Blue, Idiot Wind, Shelter From the Storm
(Maybe should have stipulated a no-Dylan rule as well …)
Pink Floyd Dark Side of the Moon
“Money,” “Us and Them” “Brain Damage/Eclipse”
Beatles – Well, you can choose several. I’ll go with Abbey Road
“Come Together,” “Something,” “Here Comes the Sun,” “She Came in Through the Bathroom Window.”
The Clash – London Calling
“London Calling,” “Clampdown,” “Train in Vain.”
The Who – Tommy
“Pinball Wizard,” “We’re Not Gonna Take It” “Overture”
Rolling Stones – Let it Bleed
“Gimme Shelter,” “Let it Bleed,” “You Can’t Always Get What You Want.” “Midnight Rambler.” (Beggars Banquet could also be considered.
Neil Young’s “Harvest”: “Old Man,” “Heart of Gold,” “The Needle and the Damage Done.”
Hendrix’s “Are You Experienced”: “Purple Haze,” “Hey Joe,” “Foxy Lady.”
(I have a feeling I’ll be coming back to this thread a lot!)
Oh! “Allman Brothers Band” with “Dreams,” “Whippin’ Post” and “Trouble No More.”
Fleetwood Mac, Rumors, “Dreams”, “Go Your Own Way”, “Don’t Stop”, “Songbird”, “You Make Lovin’ Fun”.
Oh, and “Gold Dust Woman” and “The Chain”. And let’s not forget a song that couldn’t make the cut because of length, “Silver Springs”.
“Undeniable” and “classic” are terms we could argue about.
I’ll count a song as a “classic” if it’s either a staple of classic rock radio or an instantly recognizable tune within its genre. So, even if I don’t much like a song or artist, I’ll count it as a “classic” if it meets those criteria.
So…
Paranoid by Black Sabbath has three tunes that are “classics” of the heavy metal genre: “Iron Man,” “War Pigs,” and the title track.
Are You Experienced? by the Jimi Hendrix Experience had “Foxy Lady,” “Purple Haze,” “Hey Joe” and “Fire,” all of which qualify
CCR’s Cosmo’s Factory had “Travelin’ Band,” “WHo’ll Stop the Rain,” “Up Around the BEnd” and “Lookin’ Out My Back Door.”
The Doors featured “Break on Through,” “The End,” and “Light My Fire.”
Billy Joel’s The Stranger:
“Just They Way You Are”, “Only The Good Die Young”, “She’s Always A Woman”
as well as…
“Vienna”, “Scenes From an Italian Restaurant”, “Movin’ Out (Anthony’s Song)”
I’ll go with astorian’s definition.
AC/DC - Back In Black, “Back In Black”, “You Shook Me All Night Long” and “Hell’s Bells”.
ZZ Top - Eliminator, with “Gimme All Your Lovin’”, “Legs” and “Sharp Dressed Man”.
Van Halen - 1984, “Jump”, “Panama”, “Hot For Teacher”.
Boston - Boston…pretty much every track on it, certainly “More Than A Feeling”, “Rock And Roll Band” and “Smokin’”.
Journey’s “Escape”: “Don’t Stop Believin’”, “Who’s Cryin’ Now”, and “Open Arms”
Supertramp qualifies multiple times:
Crime Of The Century - “School”, “Bloody Well Right” and “Hide In Your Shell” (and “Asylum” and “Dreamer”)
Even In The Quietest Moments - “Give A Little Bit”, “Even In The Quietest Moments” and “From Now On”
Breakfast In America - “The Logical Song”, “Goodbye Stranger” and “The Long Way Home”
Electric Light Orchestra also qualifies several times:
Face The Music with “Evil Woman”, “Nightrider”, “Strange Magic” and “One Summer Dream”
A New World Record with “Telephone Line”, “So Fine”, “Livin’ Thing” and “Do Ya”
Out Of The Blue with “Turn To Stone”, “Sweet Talkin’ Woman” and “Mr. Blue Sky.”
Aja by Steely Dan has “Josie”, “Peg” and “Deacon Blues.”
Boston with “More Than A Feeling”, “Peace Of Mind” and “Foreplay / Long Time”
Billion Dollar Babies by Alice Cooper, with “Hello Hooray”, “Elected”, “No More Mr. Nice Guy” and “I Love The Dead”
The Eagles’ Hotel California with “Hotel California”, "New Kid In Town"and “Life In The Fast Lane”
Some more recent releases:
Evanescence - Fallen - Bring Me To Life, Going Under, My Immortal
Green Day - Dookie - Basket Case, She, Welcome to Paradise, When I Come Around
Green Day - American Idiot - the title track, Boulevard of Broken Dreams, Holiday, Wake Me Up When September Ends
Nickelback - The Long Road - Feelin’ Way Too Damn Good, Figured You Out, Someday
Nirvana - Nevermind - Come As You Are, In Bloom, Lithium, Smells Like Teen Spirit
Offspring - Smash - Come Out And Play, Gotta Get Away, Self Esteem
White Stripes - Dead Leaves And The Dirty Ground, Fell In Love With a Girl, Hotel Yorba
White Stripes - Elephant - Hardest Button to Button, I Just Don’t Know What To Do With Myself, Seven Nation Army
Oops. Dead Leaves And The Dirty Ground, Fell In Love With a Girl, and Hotel Yorba are on the album White Blood Cells.
Pet Sounds - The Beach Boys; “Wouldn’t It Be Nice” “Sloop John B” “God Only Knows”
American Beauty - The Grateful Dead; “Box of Rain” “Ripple” “Truckin’”
*Ten *- Pearl Jam; “Even Flow” “Alive” “Jeremy”
Goodbye Yellow Brick Road - Elton John; many to choose from, I’m sure most people could agree on three.
*Abraxas *- Santana; “Black Magic Woman” Oye Como Va" “Hope You’re Feeling Better”
Ozzy has
Diary of a Madman: Over the Mountain, Flying High Again, You Can’t Kill Rock and Roll and Diary of a Madman. Note, you could probably either add a couple more tracks or replace You Can’t Kill RnR with another track. The whole album rocks.
Blizzard of Ozz: Crazy Train, I Don’t Know, Revelation (Mother Earth), Suicide Solution and Mr. Crowley.
Slee
Pearl Jam *Ten *
“Alive”, “Evenflow”, “Black”
R.E.M. Automatic for the People: “Everybody Hurts”; “Nightswimming”; “Man on the Moon”
I’d add “Find the River” and “Drive” to the list - hell, I’d probably add all the other songs on the album as well - but I’m a hard-core fan.
Pronounced Leh-Nerd Skin-Nerd - Lynyrd Skynyrd
“Freebird”
“Tuesday’s Gone”
“Simple Man”
“Gimme Three Steps”