As in, whenever I see Waco, Texas mentioned, I think of… well, I’m sure you know.
Same goes for Brentwood, CA. “…blood found at Simpson’s Brentwood estate…”
Columbine, CO
Pretty much any town named Springfield
Locally, I always think of Watsonville, CA as being the epicenter of the 1989 Loma Prieta (SF) earthquake, but I think that’s just me.
Dresden.
Coventry.
Hiroshima/Nagasaki.
Many others; I’m sleepy today.
Valdez, Alaska will forever be connected with the Exxon Valdez oil spill in 1989.
Ironic that the Exxon tanker that went aground on a chartered reef (Bligh Reef named after Captain Cook’s navigator) was named the Exxon Valdez. Since Valdez was the closest town and the terminus of the pipeline, the base of clean-up operations were in Valdez. So when you hear Valdez, you think of the largest oil spill off America’s shoreline.
Johnstown for the flood
Philly for the cheese steak
Chicago for World Series futility and the fart thread 
Which brings to mind Boston for the baked bean
Niagara Falls, NY.
Manassas, VA (or Bull Run if you prefer)
Independence, MO.
New York City - World Trade Center attacks
Dallas - JFK assassination
Oklahoma City 
Jonestown, Guyana for the mass kool-aid suicide.
Chernobyl for the nuclear reactor disaster.
Columbine High School was in Littleton, CO. I don’t know if there is a Columbine, CO.
I live in Bellingham, WA.
For a sleepy, quirky little town in the sleepy, quirky little part of my state north of Seattle, we seem to have garnered some pretty gruesome things to be “known” for.
Kenneth Bianchi moved north from LA after he and his cousin killed lots of women in the LA area…the “Hillside Strangler” thing? He then killed his last two victims HERE, which led to his eventual incarceration. I think he got caught HERE because in THIS town, it would be difficult to NOT be caught if you caused two women to disappear…it was pretty stupid for him to assume that the two women he set up wouldn’t have told someone they were going to house sit for someone…even though he told them to keep it confidential that he had set up this “house sitting” deal. Around THESE parts, you should realize that a person is going to tell SOMEONE what they are doing. It is only neighborly to “share,” you know?
Then the recent snipers in the Northeast lived here for a time, interacted on a pretty public basis with people in a coffeehouse, the young man went to the High School I graduated from, and they were a part of the community in many ways. Sure, lots of people here WERE suspicious of the older man, and reported it, but since he hadn’t DONE anything, the authorities couldn’t do anything aBOUT it. The young man was welcomed into the homes of TWO people I know…because he knew their kids at school. He seemed like a really good and polite young man, too…very grateful to them for opening their home to him.
So…I picked up Time magazine one day and to my great shock I saw that my town was mentioned in the very FIRST paragraph of the article about them.
Weird.
Then, of course, Seattle is known for the Space Needle, Ted Bundy and (South Seattle) the Green River Killer.
Once again, that is two things out of three that are gruesome.
This whole thing feels VERY weird if you live here.
You’re totally right… brain fart.
mudcrutch Not so much those (well, definitely not NYC) because while there are some huge things that happened there in history, they won;t be explicitly known for those events.
I don’t think that NYC will be known only for the WTC attacks.
The suggestion of Coventry (in the list with Dresden, Hiroshima and Nagasaki) is interesting as this maybe highlights a different international perspective. I suspect that if you asked people in the UK to say something abut Coventry, you’d get Coventry Cathedral and Coventry City football team as the most common answers.
To the OP, I would add Lockerbie, Hungerford, Dunblane and Aberfan.
The OP seems to be answered almost exclusively by disaster sites.
Heidelberg
Selma
Little Rock
Alamagordo
San Antonio, TX - Remember the Alamo
San Diego, CA & Perris Island, SC - Where Marines are born
I think the best candidates would be very small towns that had a worldwide famous event occur.
I propose:
Pompei - famous eruption, and nothing else will ever happen there.
Wittenberg, for Martin Luther’s theses - perhaps too obscure to qualify
Hameln (Hamlin) - pied piper
I disagree with some of the previous proposals:
Many of the cities have other associations or can potentially have something in the future. For example Brentwood has other associations for me (I live in the area) and how many people would really remember that Nicole Simpsons and Ron Goldman were killed in Brentwood?
When I hear Heidelberg, I think of college students (Somerset Maugham’s ‘Of Human Bondage’). What should I be thinking of?
Dresden - I think of porcelain dishes first and the fire-bombing of Dresden second. etc…
I agree with this proposal:
Hiroshima would definitely qualify in my book. Of course I’m not Japanese, but I imagine that even for a Japanese person the name Hiroshima immediately brings up the idea “atom bomb explosion.”
Lakehurst, New Jersey.
Living in Alabama, Id Have to say Selma. And I am sure I don’t have to say why.
Ditto.
Delft (unless you follow art or early modern science). Ghent (as in Treaty of). Nuremberg. Fort Lauderdale. Casablanca. New Orleans, more or less.
Nashville.twang!