Ok, get it off your chest - I bet there is at least one pair of songs you know of, the second of which made you think "hang on a minute! - that sounds exactly like (insert song title) !"
One of my "rip-off outrage" songs is "jerk it out" by the caesars - the verses of which are a blatant rip-off of Girls On Film. You can literally sing the lyrics to Girls On Film over it.
So to simplify - here's a suggested template:
Jerk It Out by The Caesars/Girls On Film - Duran Duran
Taxman - The Beatles/Start - The Jam (identical bass-line)
(inspired by sallabananas' Up The Junction thread)