There's a lot of overlap and some gaps, but this about the way I see it.
'20's to '50's - Delta Blues and Early Folk & Country...Robert Johnson, Son House, Woody Guthrie, Hank Williams
Mid 50's to '59 - Electric Blues and Rock 'N Roll...Elvis Presley, Chuck Berry, Johnny Cash, Buddy Holly, Howlin' Wolf, Muddy Waters
'59 to '64 - Folk Revival and Protest...Bob Dylan, Pete Seeger, Joan Baez, Phil Ochs
'62 to '64 - British Invasion...the Beatles, the Rolling Stones, the Animals, the Yardbirds, the Kinks, the Who
'65 to '66 - Folk Rock...Dylan goes electric, the Beatles' Rubber Soul, the Byrds, Buffalo Springfield, Simon and Garfunkel
'67 - The Summer of Love...Jimi Hendrix, Jefferson Airplane, Syd Barrett-era Pink Folyd, Sgt Pepper's, Janis Joplin, the Doors
'68 to '70 - Back to the Basics...the Band, Led Zeppelin, Beggar's Banquet
'67 to '72 - Proto-Punk...The Velvet Underground, Captain Beefheart, the Stooges, the MC5
'69 to '73 - Singer-Songwriters...Neil Young, Joni Mitchell, Van Morrison, Jackson Browne, Townes Van Zandt, Leonard Cohen, James Taylor
'71 to '73 - Glam Rock...David Bowie, Lou Reed, T. Rex, Roxy Music, the New York Dolls
'71 to '75 - Progressive Rock...Pink Floyd, King Crimson, Rush
'76 to '79 - Punk Rock...the Ramones, the Clash, the Sex Pistols, Patti Smith, Black Flag, the Talking Heads, Blondie
'79 to '82 - Post-Punk...Joy Division, the Cure, Siouxsie & the Banshees
'74 to '85 - Arena Rock...Queen, Bruce Springsteen, KISS (?), Journey, REO Speedwagon
'80 to '89 - MTV Era...Duran Duran and so on and so forth
'84 to '89 - Hair Metal...Motley Crue, Poison, Guns 'N Roses
'90 to '94 - Alternative Rock/Grunge....Nirvana, Soundgarden, Pearl Jam, Sonic Youth, the Pixies, REM
'94 to '99 - Powerpop, or something...Green Day, Oasis
'99 to '03 - Garage Rock Revival...the White Stripes, the Strokes, the Killers, the Black Keys
'03 to '07 - Emo...My Chemical Romance, Simple Plan, Arcade Fire
'08 to Present - Indie Rock...Beirut, the Fleet Foxes, Cage the Elephant, Mumford & Sons