I find the concept of EPs fascinating. It was never as a big of a thing in the US but there were some of course.
But in the UK EPs were a big thing until 1968. And the Beatles released a lot of EPs in the UK. Unlike the US where singles were used to sell albums in the UK albums were more often sold as products to sort of compliment singles. You made your hit records into singles and packaged up a lot of your other tracks into albums. I don't really get the logic as the US method of using a hit single to sell and album was so standard here
In the UK they regularly used EPs to package up either
4 singles (both A and B side)
OR 4 songs from an album into 4 songs packages as an EP. They would wait a few months after sales had fallen off for those singles or that album and then package them together offering a bundle basically for discounted price. The Beatles still never usually put those singles onto an LP album until they started doing some compilations and greatest hits packages (of which the first was in late 1966 and most were in the 70s).
Conversely EPs in the US were typically for something different than just packaging singles or album subsets. It was often used as a way to get more music out following an album but before they had another full album ready. Or some special versions of songs. Or when a label had limited material from a band (like Vee-Jay did with The Beatles in 1964).
The cost of an EP was pretty affordable on a per song basis. This is the prices I found for singles, EPs and LPs in the 1958-1968 period. They started to rise after that through the 70s and 80s.
single $0.98 for 2 songs A and B side
EP $1.49 for 4 songs typically but could be 5
LP (mono) $3.98 for 11 or 12 songs
LP (stereo) $4.98 for 11 or 12 songs
EPs and mono LPs were pretty much gone by 1968.
EPs were usually charted on the singles chart in the US and UK although I think the UK had an EP chart (top 10) as well.
So here are the 15 UK (counting the double EP 2x) and 3 US Beatles EPs (I'll note the specific US ones all others are UK).
Twist and Shout - July 1963 - 4 songs from Please Please Me released in March 1963
Side one
1. "Twist and Shout" 2:33
2. "A Taste of Honey" 2:05
Side two
1. "Do You Want to Know a Secret" 2:00
2. "There's a Place" 1:53
The Beatles' Hits - September 1963 - four singles 
Side one
1. "From Me to You" 1:56
2. "Thank You Girl" (originally released as the B-side to "From Me to You") 2:01
Side two
1. "Please Please Me" (originally released as a single b/w "Ask Me Why") 2:03
2. "Love Me Do" (originally released as a single b/w "P.S. I Love You") 2:22
The Beatles No. 1 - November 1963 - four more songs from Please Please MeThe cover was a version of the Please Please Me cover photo.

Side one
1. "I Saw Her Standing There" 2:55
2. "Misery" 1:47
Side two
1. "Anna (Go to Him)" 2:54
2. "Chains" 2:23
All My Loving - February 1964 - 2 songs from Please Please Me and 2 from With The Beatles
Side one
1. "All My Loving" (from With the Beatles) 2:10
2. "Ask Me Why" (from Please Please Me) 2:28
Side two
1. "Money (That's What I Want)" (from With the Beatles) 2:52
2. "P.S. I Love You" (from Please Please Me) 2:02
US EP Vee-Jay Records Souvenir of Their Visit to America - March 1964 - four songs from Introducing The Beatles released in January 1964This EP failed to chart in the US.

Side one
1. "Misery" 1:48
2. "Taste of Honey" 2:04
Side two
1. "Ask Me Why" 2:28
2. "Anna" 2:58
US EP Capitol RecordsFour By The Beatles - April 1964 - four songs from Meet The Beatles released in January 1964Peaked at #92 on the US billboard Hot 100 singles chart

Side one
1. "Roll Over Beethoven" 2:44
2. "All My Loving" 2:03
Side two
1. "This Boy" 2:11
2. "Please Mr. Postman" 2:35
Long Tall Sally - June 1964 - unique in that these four songs had not previously been released in the UK. Side one songs had been on the US Beatles Second Album in March 1964 and Side two were on the forthcoming US Something New Album in July 1964. They would finally appear on the Past Masters in LP form in 1988.
Side one
1. "Long Tall Sally" 2:03
2. "I Call Your Name" 2:09
Side two
1. "Slow Down" 2:56
2. "Matchbox" 1:58
Extracts From A Hard Day's Night - November 1964 - four songs from the film and soundtrack
Side one
1. "I Should Have Known Better" 2:43
2. "If I Fell" 2:19
Side two
1. "Tell Me Why" 2:09
2. "And I Love Her" 2:30
Extracts From A Hard Day's Night - December 1964 - four songs from the album but not in the filmThis release used the exact same title as the previous but a different cover

Side A
"Any Time at All" 2:14
"I'll Cry Instead" 2:06
Side B
"Things We Said Today" 2:38
"When I Get Home" 2:19
US EP Capitol Records - the last Beatles EP released in the US4 by the Beatles - February 1965 - all four songs were from Beatles '65 released in December 1964a nearly identical name to the previous Capitol EP which had charted, this one also charted as high as #68.
The cover reused the Beatles '65 primary photo.

Side one
"Honey Don't" 2:56
"I'm a Loser" 2:30
Side two
"Mr. Moonlight" 2:39
"Everybody's Trying to Be My Baby" 2:25
Beatles For Sale (EP) - April 1965 - the four songs were from the album of the same exact nameThe cover photo also used the same photo as the album but a different tint

Side A
"No Reply" 2:15
"I'm a Loser" 2:30
Side B
"Rock and Roll Music" 2:32
"Eight Days a Week" 2:43
Beatles for Sale No. 2 - June 1965 - another four songs from the same album
Side A
"I'll Follow the Sun" 1:46
"Baby's in Black" 2:05
Side B
"Words of Love" 2:04
"I Don't Want to Spoil the Party" 2:34
The Beatles' Million Sellers - December 1965 - this comprised 4 singles that had hit #1 in the UK and sold over a million copies
Side one
"She Loves You" 2:19
"I Want to Hold Your Hand" 2:24
Side two
"Can't Buy Me Love" 2:15
"I Feel Fine" 2:20
Yesterday (EP) - March 1966 - like the US Yesterday and Today album this looked to capitalize on the huge single Yesterday. The tracks were all from the B side of the UK Help! album but not the movie.
Side A
"Yesterday" 2:03
"Act Naturally" 2:33
Side B
"You Like Me Too Much" 2:40
"It's Only Love" 1:53
Nowhere Man - July 1966 - contains four songs from the UK Rubber Soul album
Side one
"Nowhere Man" 2:44
"Drive My Car" 2:25
Side two
"Michelle" 2:40
"You Won't See Me" 3:22
Magical Mystery Tour (double EP) - December 1967 - the last UK EP from the Beatles during their active recording period. Contains the 6 songs from the film.

Side one
1. "Magical Mystery Tour" - 2:48
2. "Your Mother Should Know" - 2:33
Side two
1. "I Am the Walrus" - 4:35
Side three
1. "The Fool on the Hill" - 3:00
2. "Flying" (Instrumental) 2:16
Side four
1. "Blue Jay Way" - 3:50
OTHERS:There was a planned EP for
Yellow Submarine that was conceived but never released.
Track Listing: Only A Northern Song, Hey Bulldog, Across The Universe, All Together Now & All Too Much
There was an
untitled bonus rarities EP included in the 1981 EP Box Set that contained all of the UK EPs.

It contained these songs in stereo for the first time in the UK:
Side one
The Inner Light 2:39
previously included on the Lady Madonna single and "Rarities" album in mono, this stereo mix was the first such available release in the UK.
Baby You're A Rich Man 3:04
previously issued in mock stereo on the All You Need is Love single and Magical Mystery Tour album, this true stereo mix was first issued on The Beatles Box for the first time.
Side two
She's A Woman 3:06
previously included on the I Feel Fine single and "Rarities" album in mono, Also issued for the first time in stereo on The Beatles Box. This stereo mix is slightly longer and includes a "1, 2, 3, 4" count-in from Paul.
This Boy 2:14
previously included on the I Want To Hold Your Hand single and "Rarities" album in mono. The sleeve claims this is the first stereo release available in the UK, but this mix was previously used on Love Songs.
This was the cover of the EP Box Set mentioned above: