The Double A-Side

On Dec. 7, 1948, RCA Victor Records released the first 45, "Pee-Wee the Piccolo" by Paul Wing with Russ Case and His Orchestra, aimed at the children's market. The company bet that its new 7-inch records would replace the standard 10-inch 78s that had dominated the music industry since the 1920s. RCA's entry into the adult market would come on March 31, 1948. Columbia Records had introduced the 33 1/3, a.k.a. the album or LP, in 1948. The 45 was RCA's answer. The speeds 78 and 33 are basically random, by the way, but you'll notice that 78-33=45.
RCA Victor released several new recordings simultaneously on that day, including "Texarkana Baby," a huge hit for country's Eddy Arnold. By May of that year, with 45 phonographs flying off the shelves, RCA's single of Perry Como’s "'A' You're Adorable" reached the top spot, the very first No. 1 on the Billboard charts for the new format.
The 45 was perfect for the new rock 'n' roll sound and tapped into a new demographic of buyers, the American teen. Due to the 45's compact size, teenagers could grab a handful of records and take them to a friend's, where they could dance the night away to their favorite tunes by Elvis, Jerry Lee, Chuck and the rest.
In the early days and even beyond, only the A-sides mattered. And it has only been with the resurgence of vinyl that collectors and music aficionados are discovering the B-side as a new collection of forgotten songs often not included on an LP. Let's call it "rediscovery," since the frugal teen buyer wanted a bang for his or her buck. 
Ah, but then there are thedouble A-sides. The Beatles, of course, had four British Double-A's (more in the U.S.): "Day Tripper/We Can Work it Out," "Eleanor Rigby/Yellow Submarine," "Penny Lane/Strawberry Fields" and "Come Together/Something." But there were plenty more; more than a hundred, in fact. Here are some of the best (not all are truly double A-sided, but two songs of equal stature):
Led Zeppelin — "Whole Lotta Love/Living Loving Maid (She’s Just a Woman)" (1969).
The LP was Led Zeppelin's domain and their music was meant to be heard that way in the new era of AOR. In fact, they didn’t even release any singles in the U.K. In the U.S. an edited version of "Whole Lotta Love" made the U.S. top 10.
Crosby, Stills & Nash — "Suite: Judy Blue Eyes/Long Time Gone" (1969).
CSN released these two tracks from their self-titled Atlantic album. Stephen Stills' acoustic ode to girlfriend Judy Collins made for a marked contrast to David Crosby's rocker.
The Band — "Up on Cripple Creek/The Night They Drove Old Dixie Down" (1969).
From The Band's landmark sophomore album, this was the beginning of what today we often call Americana.
The Monkees — "I'm a Believer/(I'm Not Your) Steppin’ Stone" (1966).
The B-Side here only made it to No. 20 (with "I'm a Believer" a No. 1 smash), but what a B-side it is. Paul Revere and the Raiders had cut the Boyce Hart song previously on an LP, but it was the Monkees that had the hit. This is the list's only entry not from 1969.
Another that didn't even make the list...The Guess Who — "Laughing/Undun" (1969).
Nowhere near the top spot, but each of these rate right up there in my book. "Laughing" went to No. 10 and "Undun" to No. 22 in the States.  Creedence Clearwater Revival — "Proud Mary/Born on the Bayou" (1969).
Did you realize that CCR never had a No. 1 single? That’s right: On five occasions they reached No. 2. Like The Beatles, Creedence embraced the Double A-Side with "Bad Moon Rising/Lodi," "Down on the Corner/Fortunate Son," and "Travelin' Band/Who'll Stop the Rain."
The Rolling Stones — "Honky Tonk Women/You Can't Always Get What You Want" (1969).
You want two sides of perfection? You can get that all over The Stones' discography: "Ruby Tuesday/Let’s Spend the Night Together," or "Street Fighting Man/No Expectations" but it just does not get any more classic than the gritty "Honky Tonk Women" pairing up with "You Can’t Always Get What You Want."