Starting with bands such as propaghandi and the vandals, true pop punk today is much more accessible and centered around bands such as Fireworks, Transit, The Wonder Years, Polar Bear Club, and to a lesser extent Title Fight.
New Found Glory is considered to be the band which brought Pop Punk into the spotlight and influenced all of the bands above to some extent.
Fall out boy, Sum 41, Simple Plan, ect. are not pop punk. They are no different than mainstream top 40 artists like brittney spears or miley cirus. They use the same gimmicky pop hooks and overproduction except with guitars and awful fucking clothing.
sum 41 is NOT pop punk.