Alkaline Trio are definitely pop punk. Besides the pop punk sound they've opened for Blink (Enema of the State
tour, I believe? Or Maybe it was TOYPAJ
?) and shared a producer with them.
And if you've never head of/listened to bands like Descendents, Mister T Experience or Lawrence Arms then youhave a whole great world of pop punk ready for you to listen to.
A lot of people end up getting into pop punk through the Drive Thru style and I have a lot of love for those bands but the Lookout!, Asian Man and Fat Wreck styles (to name a few) shouldn't be overlooked.