Google Maps Mashup?

I've seen a widget-type thing, Google Maps mashup, where visitors to a website enter their zip code or address or something else, and then the mapsite generates a Google Map with flags for everyone's location. Some people put this as a plug-in sorta thing on their blog page, or webcomics do it too. But I can't find it! It's a famous one and I can't remember the name, and Google search isn't helping me.

Anyone know the sorta thing I'm thinking of? If so, give me the name and link me up!