Parts of Akon's "Right Now (Na Na Na)" sounds like DJ Sammy's "Heaven."
The drum beats in Kelly Clarkson's "Already Gone" and The All-American Rejects' "The Wind Blows."
Beyoncé's "Sweet Dreams" has beats (and especially they "yo!"s) sounds like Raven-Symoné's "Green."
The intros to Britney Spears' "Radar" and Christina Aguilera's "Keeps Gettin' Better." (Especially in live versions.)
Ashley Tisdale's "Masquerade" and Fall Out Boy's "I Don't Care" are similar at parts.
The Fray's "Never Say Never" has parts that resemble their previous hit, "How to Save a Life."
Gavin Rossdale's "Love Remains the Same" and David Cook's "Light On" have some similarities.
O.A.R. "Shattered (Turn the Car Around)" and Carolina Liar "Show Me What I'm Looking For" have almost the same instrumental.
Sean Kingston's "Fire Burning" and Kat DeLuna's "Unstoppable" are the same song, with different lyrics and singers.
Theory of a Deadman "Not Meant to Be" and Avril Lavigne/Leona Lewis "I Will Be" kind of mesh together, especially in the bridge.
Except Already Gone (just because of Kelly's live version) 
Kinda right
When I first heard it, I was like, are you serious?