CSS-Tricks #34: Integrating and Customizing Google Maps
Google maps, with all the dragging and zooming and satellite view and all, is my mapping service of choice. Google offers an free API for their maps so you can integrate them right onto your site. Set you own default location, zoom level, widgetry. Even add your own markers with custom balloons. Remember though, if a map and directions are vital to your site, nothing beats some "plain English" directions.