To make things more interesting in terms of popularity, I've decide to search various genres under eBay's music section along with entering the year. The years ending in 0 are a bit tricky since it can often mean shorthand without the "s" at the end, though it can be easy to tell most instances. That said, I've decided to look at some popular generes that peak in the '50s/'60s and breakdown their popularities.

Doo Wop: A CD entitled "The Complete Story of Doo Wop" traces the origin to 1939. However, there wouldn't be a notice increase in the number of titles available until 1953 (just under 100), around the time some whitebread stations played the crossover music during the late night. It would then steadily grow, reaching its peak around 1958 (the big "tailfins" year), taking a bit of a dive in the wake of Payola in 1959, recover in 1960, gradually decine through the early '60s (though still remaining above 1954 levels through '63). Not surprising, one of the biggest drops in Doo Wop titles available is between 1963 and 1964, a fall of 55% showing that Beatlemania and even Motown made this genre too old school. But up through 1968, there were always a few laggards in the hopes of extending their careers. Then in 1969, another 55% drop fueled by the vast splicing of musical genres and new sounds that peaked with the psychedelic movement. Any Doo Wop in the 1970s and beyond was just the occassional retro track, and was nowhere nearly as popular as it was.

Rockabilly: Rooted in Hillbilly and Boogie in the 1930s and early 1940s, the first mention, like Doo Wop above, is for a Chicago CD boxset starting the era at 1945.  The earliest single Rockabilly title found is Sam Nichols "Keep Your Motor Hot" from 1949, the only title found from that year. That said, Rockabilly didn't start to become a bit noticeable until 1954 with 18 results found. From then, Rockabilly enjoyed remarkable growth through 1957, its peak year of popularity with the number titles available doubling each year. That said, Rockabilly was never quite as profuse as Doo-Wop (only about 35% of titles at its peak compared to Doo Wop) and faded quicker, especially between 1959 and 1961.

Surf Rock: A bit trickier to define due to some songs simply having "Surf" in their title. The first Surf records appear in 1958, with slow, steady growth through 1962. Surf then had a peak in 1963 at a level similar to Rockabilly's in 1957, thanks to the rise of the Beach Boys. That said, it did not last long. 1964, while still over twice 1962's "eBay popularity", still had over a 40% drop compared to 1963 (thanks again British Invasion), another big drop in 1965, one last moment in the sun in 1966 thanks to Pet Sounds, and then basically buried into the stand in 1967 as LSD was preferred.

The "Twist" Craze: While not a genre, in 1962 there were more titles tagged with "Twist" than Rockabilly and Surf ever were at their peaks! The original Hank Ballard released in 1959, followed by Chubby's in '60, along with his seuqels in 1961. There was a big drop-off of nearly 70% in 1963, a drop-off that could have been bigger if not for the Beatles' Twist and Shout which keeps it going through 1964. Pretty much toast by 1965 though.

Girl Groups: A bit tricky to define since many good examples lack the "girl group" tag. However, the earliest records are the Hearts "All My Love Belongs to You" and The Burton Sistes' "Wabash Blues" in 1955. 1957-58 saw a noticeable rise thanks to The Chantels and the Shirelles' first hits. A bit of a drop thanks to Payola in 1959, 1960 saw a new peak in popularity thanks to the Shirelles. The peak was 1963-64.

British Invasion: A bit skewed thanks to The Beatles' Red Greatest Hits Album forcing 1962 too high, the real boom comes in 1964, with a popularity index nearly double Doo Wop's peak. While 1964-67 were the peak, unlike other genres, there was (and is) still a sizable following of releases and new albums. A noticeable rise occurs in 1987-88 due to the Beatles' albums appearing on CD for the first time. Its why that so many songs lasted decades on the radio and many are still played today unlike the former genres listed. It wasn't until the early '90s that its relevance started to fade a bit, and that was only due to a generational shift in music. And even then, 1995 brings another spike due to some "new" Beatles tracks and the Britpop movement's peak.

Psychedelic (Psych): A few covers/songs in the early '60s have primitive elements of what became the psychedelic style, such as Dale Hawkins' 1961 "Let's All Twist" (See The "Twist" craze above) and the Astronauts 1963 "Surfin' With" album (See Surf). 1965 would be the year that the Psychedelic sound would start to emerge (Thanks Rubber Soul and Aftermath). 1966 continued 1965's trend, more than tripling in search hits compared to the previous years. While not as dramatic of a sharp increase, 1967 more than doubled 1966's popularity and by that point was more popular than Doo Wop had ever been. Even 1968 still registered more than a 70% rise over '67. 1969 was the peak as you might expect with Woodstock. 1970 registered a bit of a drop, but was still around 1968 levels in popularity. Even 1972 was still comparable to 1967's amount of titles available. It wasn't until around 1976-77 that its popularity finally had succumed to other genres such as Punk, Disco, and later New Wave. A cult following still lingers.

Interesting analysis  :)  Many of the major genres are represented.  There are a few others I'd be interested to hear this type analysis about, for example garage band rock and Motown soul.  But you've included a really good cross section.