Geocoding - In order to plot using most mapping services you'll need to map an address to lat/long coordinates. Here are some examples/services:

http://groups.google.com/group/Google-Maps-API/browse_thread/thread/21478ab8e84b0f01/0a5b167ffae4bacd?lnk=st&q=Geocoding+yahoo&rnum=1#0a5b167ffae4bacd
http://mapbuilder.net/demo/yahoo.geocode.php
http://developer.yahoo.com/maps/rest/V1/geocode.html