For my money, they are:
Stairway to Heaven (natch)–Led Zeppelin
I don’t think this little ditty needs much explanation. It’s timeless classic that I never get tired of. It’s just incredible, and with good reason.
Rock and Roll–Led Zeppelin
I love how fast this song flows. As soon as it starts up my heart starts racing. The hard edge it has and the great mix of lyrics and instruments. I hate that Cadillac basterdized it and now people only know it that way.
I love this one unplugged more, but it is incredible. It’s intense with great lyrics. Great flow. Especially unique because a lot of love songs by a guitar god don’t work. This one does.
Sweet Home Alabama–Lynard Skynard
Probably the single most recognizable first 2 seconds to any song ever made. Great party song. Always appreciated when it plays. Just love it.
Free Bird–Lynard Skynard
This one is controversial. You either love it or hate it. I love it. So there. It’s my list. I love the lyrics and how they work together so well. I personally find the guitar work amazing. This song is one (of many) reasons I always wish I could play the guitar.
Pride and Joy–Stevie Ray Vaughn
This intro might be neck and neck with Sweet Home Alabama on recognition. Great song. Love/tribute song that works well. Tons of guitars (I love guitars) and it has a blues feel and I love the blues too. As soon as this song starts I start moving. It has great energy.
I love this song. Great drinking song. (Actually most of these are) I have a hard time understanding the meaning of all of it though. But that’s OK. I still love it. The way the words tie to the instruments is great. And the pace works extremely well.
American Pie–Don McLean
You can’t be surprised about this one right? I mean, come on. Great song. Great info in the song. You can debate what he was talking about in the song forever. Plus, it’s easy to remember the lyrics to when you need to sing kids to sleep at night.
Honorary mention but not quite good enough
After Midnight, Knockin’ on Heaven’s Door, I Shot the Sheriff–Eric Clapton
White Room and Crossroads by Cream
A ton of other Led Zeppelin and Lynard Skynard songs.
Misc songs by Santana, Jimi Hendrix and the Doors.
They are called classics for a reason.
PS. My cutoff point was Van Halen. Van Halen is NOT classic rock. They are too new to be considered classic rock.