Yea man I went to warped tour a few weeks back, and I saw Four Year Strong. Since then I downloaded their whole discography and was amazed with their stuff. Your friends band isn't bad either. I would consider seeing them live if they were from my area.
Check out Featherweight, Daylight, Basement. Title Fight if you have yet. All solid "pop-punk" bands if you want to refer to them as such, have an emo sound to them. Besides that I dig Saves the Day, Taking Back Sunday, Brand New, Bayside, ect