The other day I heard the Supremes' 'Up The Ladder To The Roof' for the first time in ages, and it stuck in my head as an earworm. Not a problem - it's a great tune.
But, as I was riding through Tooting, I found I was actually tracking Prince's 'Little Red Corvette'. Switching between the two, it's pretty obvious that the main hook has been shamelessly lifted, and I'm amazed that Prince managed to get away with it, as it's a lot closer than some of the famous cases which have succeeded.
EDIT: Thank you, ESL, for the giggle you provoked when you pointed out the irony that I started a new thread on plagiarism