Punk

.Refused

.Dead Kennedys - Holiday In Cambodia

.The Clash

.Sex Pistols

.The Misfits

That's all I like really.
 
NOFX - White Trash, Two Heebs & a Bean or Punk in Drublic
The Lillingtons - Death By Television
Dead Kennedys - Give Me Convenience or Give Me Death
Minor Threat - Discog
Refused - The Shape of Punk to Come
The Descendents - Somery
The Queers - Don't Back Down
 
Not technically punk themselves, but MC5 and Iggy & The Stooges are essential proto-punk worth checking out if you don't have anything by them already.
 
The Misfits
Dead Kennedys
Black Flag
Minor Threat
The Ramones
The Clash (early stuff)
Agnostic Front (early stuff)
Discharge
The Exploited
GBH
The Vandals
Guttermouth
Choking Victim
Leftover Crack

I'm not so into the whole retro-street punk thing (a la The Casualties, The Unseen, The Virus, Cheap Sex, etc.). Some of these bands are alright musically but, like retro-thrash, it almost becomes more about the fashion than anything else.
 
Dead Kennedys
Wire's debut album (a hugely underrated punk classic)
Bad Religion
The Misfits (before Glenn Danzig left, not the 'reformed' Misfits)
Black Flag
 
My favourite punk band is definitely Refused...so I'd recommend both "Songs to Fan the Flames Of Discontent" and "The Shape of Punk to Come". I'd also recommend Modern Life Is War, Dropkick Murphys, Transistor Transistor, and The (International) Noise Conspiracy (Dennis from Refused is their vocalist).
 
I like Refused but they influenced a lot of really shitty bands to come (aka a lot of the screamo/emo shit you hear today).
 
I like how so much of the bands listed are grind/crust. Old AFI/7 Seconds/Buzzcocks/Dead Kennedys/Gallows/Rites Of Spring are all kinda good, imo.