Listen to the theme of the bridge of Smith's "Stay With Me" (from 2:10-2:32 of the video). It sounds almost exactly like the beginning violin measures of Bentley's "Gonna Get There Someday" heard right at the start of the song.
The verse vocal melody to Eric Carmen's pop ballad All by Myself (released December 1, 1975) was based on the second movement of Sergei Rachmaninoff's Piano Concerto No. 2 in C minor, Opus 18 (composed 1900-1901). All by Myself is a half-step higher. [Thanks to Grayson Dantzic for suggesting this one!]
The synth bass hook to Iggy Azalea's Fancy (released February 17, 2014) is similar to the wah-wah guitar hook to the Grateful Dead's Shakedown Street, from the band's album of the same name (released November 15, 1978). Fancy's riff is in the key of C minor and has the pattern b3-2-1-5-5-b3-2-1, while Shakedown Street's riff is a whole-step higher, in the key of D minor, and has the pattern b3-2-1-b3-b3-2-2-1. [Thanks to Andrew Zucker for suggesting this one!]
Miley Cyrus' controversial party-all-night hit We Can't Stop (June 3, 2013) bears a strong resemblance to MC Hammer's cover (released March 16, 1990) of the Chi-Lites 1971 soul classic, Have You Seen Her. Both songs are in the key of E major, have similar background vocal harmonies, and WCS follows a I-iii-vi-IV progression, while HYSH follows a I-iii-IV-V progression.
The verse vocal melody to Colbie Caillat's Try (released June 9, 2014) echoes the signature repeating melody to Carol Of The Bells, composed by Mykola Leontovych in 1924 with lyrics by Peter J. Wilhousky. Both Try (in Bb minor) and Carol Of The Bells (Pentatonix's version of the popular Christmas carol is in C minor) emphasize the root, second and minor third of the key (as does Pink Floyd's Hey You), compare Try's line: "Put your make-up on, get your nails done, curl your hair" with COTB's "Hark hear the bells, sweet silver bells, all seem to say, throw cares away." Rhythmically, Caillat's verse vocal melody is also reminiscent of the verse vocal melody to "All For The Best" from the Broadway musical Godspell (around 1:16 with the line "some men are born to liberties, doing what they please").
As a musician and composer, I’m often struck by similarities between pop songs. If you’ve ever listened to a tune on the radio and thought to yourself, “this sounds really familiar,” or “what does this melody remind me of,” (or more bluntly, “this song is a rip-off of …”) then you have shared in the experience.