Classic and throwback only, and mostly US punk (and more evolved from the 80s DC punk scene rather than the SoCal punk scene). I hate the fucking Sex Pistols. Bunch of diva douchebags. Seriously, punk is a whole lot about principle. The Sex Pistols were/are frauds. I do love The Clash, though. No matter how big they got, they were still a great bunch of guys. Joey Strummer is a legend.
I like the Minutemen, Fugazi, Sonic Youth (I really consider noise rock a form of punk), Minor Threat, Black Flag (the very early stuff), Bad Religion, Husker Du, and that sort of punk. The Dead Kennedys were great too. Jello Biafra would go out of his way to help artists he believed in. Punk is a lot about the community that supports itself to me.
More recent bands I like are Ted Leo (he's been with a few bands. Right now, it's Ted Leo and the Pharmacists), No Age, Fucked Up, Titus Andronicus (holy shit, is The Monitor an outstanding album or what?)...
Edit: I feel like linking to a Titus Andronicus song because it is amazing.