Quoted from Slave Trader

Lennon stole the riff to "I Feel Fine" from Bobby Parker's "watch your step", and the "Day Tripper" riff he brutally took from Bo Diddley's "Road Runner"  

Quoted from Andy Smith

and nobody knew at the time???  

Hey ST - I hear it differently ... to me the Bo Diddley riff is much more of a generic blues/rock riff than something like "Day Tripper". Paul's bass line in "I Saw Her Standing There" uses that progression, and a million other songs, even the "Courageous Cat" cartoon is pretty close.

Bobby Parker's "Watch Your Step" really does sound a fair amount like "I Feel Fine", but you know, it too is a pretty generic one. Listening to The Allman Brother's band song (title? ... key line is "There's a man out there, might be your man, I don't know") from the Live at the Fillmore album - now THAT is a ripoff of "Watch Your Step".

The Beatles continued to absorb influences long after their initial success, often finding new musical and lyrical avenues by listening to their contemporaries. Among those influences were Bob Dylan, who influenced songs such as "You've Got to Hide Your Love Away" and "Norwegian Wood (This Bird Has Flown)".[103] Other contemporary influences included the Byrds and the Beach Boys, whose album Pet Sounds was a favourite of McCartney's.[104] Beatles producer George Martin stated that "Without Pet Sounds, Sgt. Pepper wouldn't have happened... Pepper was an attempt to equal Pet Sounds."[105] After Sgt. Pepper was released, Beach Boys' leader Brian Wilson was so despondent that he went to bed for months.[106]

Along with studio tricks such as sound effects, unconventional microphone placements, tape loops, double tracking and vari-speed recording, The Beatles began to augment their recordings with instruments that were unconventional for rock music at the time. These included string and brass ensembles as well as Indian instruments such as the sitar as in "Norwegian Wood (This Bird Has Flown)" and the swarmandel as in "Strawberry Fields Forever". They also used early electronic instruments such as the Mellotron, with which McCartney supplied the flute voices on the intro to "Strawberry Fields Forever", and the ondioline, an electronic keyboard that created the unusual oboe-like sound on "Baby You're a Rich Man".

Beginning with the use of a string quartet (arranged by George Martin with input from McCartney) on "Yesterday" in 1965, The Beatles pioneered a modern form of art song, exemplified by the double-quartet string arrangement on "Eleanor Rigby" (1966), "Here, There and Everywhere" (1966) and "She's Leaving Home" (1967). A televised performance of Bach's Brandenburg Concerto No. 2 directly inspired McCartney's use of a piccolo trumpet on the arrangement of "Penny Lane". The Beatles moved towards psychedelia with "Rain" and "Tomorrow Never Knows" from 1966, and "Lucy in the Sky with Diamonds", "Strawberry Fields Forever" and "I Am the Walrus" from 1967.

http://en.wikipedia.org/wiki/The_Beatles