There are so many that come to mind from many great bands. Besides the obvious ones from Page and Co., I would also nominate from Zep:
Bring It On Home (after the bluesy, low key intro from Planty and JPJ, when all hell breaks loose).
Communication Breakdown.
Custard Pie
The Bomber - James Gang
Space Cowboy - Steve Miller Band
Bastille Day, Fly By Night - Rush
Young Man Blues - The Who
Honky Tonk Woman, Street Fighting Man, Start Me Up, - Stones
Go All The Way - Rasberries
Ventura Highway - America
I Want To Tell You, Drive My Car - Beatles
Ain't Talkin' 'Bout Love, Beautiful Girls - Van Halen
Blowin' Free - Wishbone Ash
Beginnings - Chicago (it's such a breezy intro)
So You Want To Be A Rock 'N' Roll Star - Byrds