The Locator module displays a filterable map of locations. You can choose whether to show all locations on load, or enable auto geocoding to filter the list based on the visitor's location.
SilverStripe Locator on Github.
Create a Locator page in the CMS. Locations are managed under the Locations tab in the CMS via Model Admin. Simply enter the name and address of each location, and they will appear on the map.