You can make feed Google Maps a set of latitude/longitude points trivially using KML. Just type the URL of your KML file into the search field on google maps, and it'll show up.
To geocode zip codes (convert them to lat/lon pairs), you can hit http://geocoder.us/service/csv/geocode?zip=95472
Earlier this month, Metus did a post asking for LW-ers locations. I thought it would even more useful to have this information in visual format, so I created a Google map. You can access it on the website below. Unfortunately, I am terrible at this post-writing interface, so I can't get the image of the map to load onto here. You'll have to click the link to view it.
Original Post: http://lesswrong.com/r/discussion/lw/8sm/where_do_you_live_meetup_planners_want_to_know/
(If you haven't filled out the poll yet, please do it! If more people submit their location info, I'll add them to the map.)
These are only for US locations that had a 5-digit zip-code, or a city name. I may or may not map the other countries. If someone else wants to volunteer, send me a message, and I'll add you as a collaborator to the map, so you can edit.