c# geocode addresses to latitude/longitude

Looking for someone to integrate some code into an existing windows service or start a new windows service project... Basically, I have a SQL table with U.S. addresses.? I need you to? populate fields for its latitude and longitude. So the major part of the project is to take the address and hit google or geocoder or yahoo or some other service (looking for recommendations but I am fine with google) and store the lat/long data.. Thats it, but there are about 50,000 addresses to geocode so you may need to throttle the speed of your code.? ( I will also try to contact the web service we decide on to see if I can open up the limitations ). The code should run once a day and pick up the data for any addresses that does not already have the lat/long information stored... this project is c#/.NET 2.0/SQL Server 2005. I can supply you the shell for the windows service and access to my staging server.