Did The Beatles ever record with other artists?

Brian Epstein famously became aware of The Beatles when a young customer asked for a song recorded in Germay,"My Bonnie", by Tony Sheridan and The Beatles.  This disc would prove to be unique on two counts.

•  It was the first non-bootlegged recording.
•  It was also the only time they conceded top billing to another artist. 

In their subsequent recording career over a hundred people performed on official Beatles releases. These included major contributions to specific recordings - like Andy White's on the "Love Me Do" (single) to various wives, girlfriends and pals providing background harmonies. Even biographer Hunter Davies gets a walk-on vocal, deep in the chorus of All You Need Is Love"^[42]

The house rule was that only band members were credited. This even applied to star names - Eric Clapton on The White Album, for example. Only two exceptions were made in the entire 1962 -1970 discography. 

Billy Preston 

Billy Preston came close to joining The Beatles in 1969. He added keyboads/Hammond organ to several track. This is formally acknowledged on "Get Back/Don't Let Me Down" (credited to The Beatles with Billy Preston). 

Anil Bhagwat

In April 1966 George Harrison was scheduled to record the pioneering "Love You To". On the morning of the session he informed Abbey Road that he would need someone to play the tabla - a two handed Indian drum.

For once this was a missing entry in George Martin's encyclopedia of session players. As ever, however, Martin found a solution. That afternoon Anil Bhagwat, a young engineering student, was collected from his flat in Earls Court in a chauffeur driven Rolls Royce. His contribution to the recording would earn him a name-check on the back cover of Revolver - full story here.